Pros:1) Retains image sharpness2) Warmer color cast (which I prefer)3) Higher contrast than Freewell4) Larger range ND range than Freewell5) Build quality better than Freewell6) Better carrying case than FreewellCons:1) Each ND stop does not have a hard stop or even a numeric indicator so you're not sure if you are on ND 8 or ND 16. This can be a con for some but for my use it is not a big deal as I primarily shoot video and use a monitor to gauge my exposure and just rotate the ND until exposure is correct.2) Filter does not have a hard stop when it reaches 400 ND and you can keep rotating it till you get the X pattern.I'm comparing this filter to Freewell ND mist version since that seems to be the most popular ND filter being used especially in the wedding videographer circles.In terms of overall build quality I want to say the K&F filter definitely feels a lot better. Even the overall packaging makes you feel like you bought a premium product. I really like the rubberized coating they use. It feels very premium and it has a good weight to it. The anodized orange indicator is nice and allows you to adjust the ND stop easily. The case that comes with K&F's filter is much more useable and compact compared to the bulky plastic cases that freewell gives. (There was a time thatfreewell's filters wouldn't even fit their case if you installed the magnetic cap which was a huge oversight on their part although I do wish K&F had a magnetic cap as well since those are the best IMO)I am primarily a video shooter and I was hoping that the filters would have similar color casts but unfortunately they don't. It's not hard to fix this in post but still would have been nice if they did match as I have multiple cameras. I do however prefer K&F's color cast as I tend to like warmer images. I also like the halation on this filter more than I do the freewell. If you look at the image where I put the two side by side the K&F is more contrasty and the light spread is kept where it should be and not across the entire image like how the freewell does it. This looks a lot more natural to my eyes. In terms of sharpness I could not see a distinct difference between the two. Both look excellent.Biggest gripe that I see other people having is the fact that there is no indicators on the filter aside from the first ND2 and ND400. The rest of the stops are indicated by dots. I don't know why manufacturers create an excellent product and then do these kinds of small short cuts. Although for me in real world use this probably wouldn't affect me, it did make testing the two different filters a pain. This is the reason why I have only included one comparison shot because I could only test the ND2 on both filters as that is the only two ranges that are clearly marked on both filters.At the end of the day in spite of some of it's shortcomings the filter does do an excellent job of what it is supposed to do. Cut light without messing with overall image sharpness or colors and give it that nice "cinematic" glow and I honestly think it does it better than Freewell. Thumbs up from me and will be using it at my next paid gig.

This filter is very made of aluminum, slim and very light. Very well constructed.
Because this filter is 52mm , but designed to fit a 50mm size lens, you will not be able to :
1. attach your lens cap (maybe a 52mm lens cap would fit)
2. attach your lens hood
3. attach any other filters to this one. You are able to attach 50mm filters to your lens, and then stack THIS one onto those filters. I did this with my CPL filter, but found it difficult because I had to rotate the CPL , and then rotate the Variable ND filter, so I removed the CPL for now.
Also, I need to investigate whether it is even advisable to use a CPL and ND together because of the low-light.

It is really a nice feature of this filter to incorporate 1 to 11 stops on this one variable filter. It makes it easy to dial to the stop that you want to use, but I found it a little confusing. The stops are labeled with Min on one end, Max on the other , and 8 dots in between.
So I'm not really sure what dot corresponds to what ND stop, there are supposed to be 11 stops, but there are only 10 markings.
Also , there is no lock at the beginning or end of the 10 stop markings.

Anyway , I've been experimenting and getting to learn how to use it.
I see how it it very convenient to have only ONE Variable filter, instead of several. Much less exptensive, much less complicated. But it is going to take me a little bit of time to learn how to use it efficiently.

I've used it once and I paired it with a 10 stop ND filter with this and I was able to set my camera set at 30 seconds, f11 and ISO 50 in the middle of the day but with the 10 stop I could only get it to 10 seconds, f11, ISO 50. I was surprised to see that when I got home to edit the photos there was no noticeable loss in sharpness with both ND filters on and this being a variable ND filter they're notoriously known to be less sharp than a constant ND filter. I can't wait to test this out on a waterfall but being that it's summer in San Diego right now I'll have to wait to try it out but along the coast I prefer the 10 stop ND filter and being able to drag that shutter longer. The front of this variable ND filter is quite large so your lens hood won't fit on there which can be an issue with unwanted lens flares but the K&F 10 stop ND filter I used with this you're able to mount the lens hood still. I received this filter free of charge to test it out so take my review with a grain of salt but if you do choose to get this I highly recommend getting a 10 stop as well because you'll be limited to 2-3 second shutter speeds with this alone at it's darkest setting in the middle of the day where the sun is bright like it is here in Southern California. I forgot to mention that there are notches on the side and tells you the minimum - maximum darkness and each stop between so there isn't any guess work involved but I do like the fact that I was able to set my settings I wanted and just rotated the front element until my camera read that I was properly exposed.

I'm not ready to purchase an expensive 10 stop ND 100mm filter system yet. So I want to try this one out. The picture quality is solid for the money. Pic 1 (no filter), Pic 2(this product), Pic 3(K&F 40-1, 10 stop ND). Obviously, this is a big step up from plastic one (pic 3). In pic4, the pin holding the filter holder hinge was so loose. If you lose the pin, the filter holder become useless. The pin fell off when I first open the box. I didn't realize that until I tried to put the filter holder on my z6. Therefore, I decided to blue tape it to prevent the pin from falling out. I think it is a good buy if you are a amateur photographer.

This is tough to beat. Not only do you get a 100mm GLASS (not plastic) 10-stop ND filter, but you also get the filter METAL mount and multiple METAL lens adapters. Even if you need to buy step-up/down adapters because the ones included do not fit your lenses, this is still a bargain. Even though this comes in at well below the price of other 100mm 10-stop filters (without the mounting system), it performs excellently.

My unit doesn't produce any noticeable color cast, but I also shoot solely in RAW, so a color cast wouldn't be an issue anyway. The case for the filter is firm, so I don't worry about it very much when it's in my camera back, and the soft lining keeps the filter safe from scratches (so long as nothing coarse gets inside, of course). Better still, the filter mount features a second slot should you wish to use additional 100mm filters (e.g. graduated filters). I point out the size because this is the "standard" in these filters, rather than the more common 80-something mm ones you see in comparably-priced square ND filter bundles that use smaller, cheaper plastic filters instead.

The only issue I found, and this is really just nitpicking at this point, is that the filter mount never really feels very securely attached to the lens. The filter and mount won't fall off if the camera is moved or tilted forward, but the mechanism that attaches the mount to the lens adapter could be a bit tighter fitting in my opinion. Nevertheless, great product at a great price. Anything "better" will be considerably more expensive, and even then, how much "better" will it be?

Pros:

1) Retains image sharpness
2) Warmer color cast (which I prefer)
3) Higher contrast than Freewell
4) Larger range ND range than Freewell
5) Build quality better than Freewell
6) Better carrying case than Freewell

Cons:

1) Each ND stop does not have a hard stop or even a numeric indicator so you're not sure if you are on ND 8 or ND 16. This can be a con for some but for my use it is not a big deal as I primarily shoot video and use a monitor to gauge my exposure and just rotate the ND until exposure is correct.

2) Filter does not have a hard stop when it reaches 400 ND and you can keep rotating it till you get the X pattern.

I'm comparing this filter to Freewell ND mist version since that seems to be the most popular ND filter being used especially in the wedding videographer circles.

In terms of overall build quality I want to say the K&F filter definitely feels a lot better. Even the overall packaging makes you feel like you bought a premium product. I really like the rubberized coating they use. It feels very premium and it has a good weight to it. The anodized orange indicator is nice and allows you to adjust the ND stop easily. The case that comes with K&F's filter is much more useable and compact compared to the bulky plastic cases that freewell gives. (There was a time that
freewell's filters wouldn't even fit their case if you installed the magnetic cap which was a huge oversight on their part although I do wish K&F had a magnetic cap as well since those are the best IMO)
I am primarily a video shooter and I was hoping that the filters would have similar color casts but unfortunately they don't. It's not hard to fix this in post but still would have been nice if they did match as I have multiple cameras. I do however prefer K&F's color cast as I tend to like warmer images. I also like the halation on this filter more than I do the freewell. If you look at the image where I put the two side by side the K&F is more contrasty and the light spread is kept where it should be and not across the entire image like how the freewell does it. This looks a lot more natural to my eyes. In terms of sharpness I could not see a distinct difference between the two. Both look excellent.
Biggest gripe that I see other people having is the fact that there is no indicators on the filter aside from the first ND2 and ND400. The rest of the stops are indicated by dots. I don't know why manufacturers create an excellent product and then do these kinds of small short cuts. Although for me in real world use this probably wouldn't affect me, it did make testing the two different filters a pain. This is the reason why I have only included one comparison shot because I could only test the ND2 on both filters as that is the only two ranges that are clearly marked on both filters.

At the end of the day in spite of some of it's shortcomings the filter does do an excellent job of what it is supposed to do. Cut light without messing with overall image sharpness or colors and give it that nice "cinematic" glow and I honestly think it does it better than Freewell. Thumbs up from me and will be using it at my next paid gig.

Great value 10 stop filter which competes with filters a lot more expensive and is well made. I have used it on seascapes and waterfalls with no colour cast and image quality is excellent. Why spend more. Recommended.

This filter can compete against the biggest brands in the business. It has exceptional optical clarity and is a true 10 stop ND filter. I use this filter for long exposure shots, particularly nature shots with running water. However, there are many uses.

The overall build feels like quality throughout. This series from K&F knocks it out of the park and is a bargain for the level of quality. Easy to recommend.