A long time ago I started looking for filters for my Canon camera which I now have with a 77mm Sigma 17-50 lens. And since I'm not a pro or anything like that, spending some money on filters and then giving them a more recreational use gave me one thing. So I started looking at 77mm filters cheaper and buying these.
In the box you have three filters, a purse to carry these filters without being filled with dust and a brush to clean them.
Filter:
The first is an ND 4 filter, typically used for longer exposure photos. In the use I've given it has given me good image quality with no rare tint too obvious. Nothing that can't be easily corrected with a little color retouching.
The second is a polarizing filter, the intensity of which varies by rotating the filter itself. This is mainly used outdoors to remove unwanted reflections or increase the contrast of landscapes. In this case it's quite dark, so you can also run the times of the ND filter. Here we already find a little more vignetting than in the previous filter, perhaps because this is variable instead of being a fixed filter as in the previous case.
The third is the typical ultraviolet filter, which is usually recommended more than anything else to avoid rubbing a lens, which costs a lot more than the filter itself. The pocket: okay,
it
's just functional and corresponds to what it serves. The 77mm filters I bought in my case fit easily and are great.
Brush:
A little like a little like a little, it's functional. You have two endings. One end has a silky finish and the other end is more of a regular brush with hair.

In conclusion, if you don't want to spend a lot of money on filters these will help you save and you'll have three pretty good value than what other brands would cost for just one.

I got the 77mm to fit my 24-70 f2.8 lens. This seems to be a really well made filter. Turning of the ND tabs is firm but butter smooth. Then you turn the whole outer frame housing for the polarizer adjustment. That is also firm, maaaybe just a little too firm as turning clockwise can actually start unscrewing the whole assembly from the lens! It does have a serrated inner lip to ease with tightening it to the lens.

Recommended!!

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?

This is my first variable ND filter and Im very happy with it. I got the 77mm version because its a very common size and I already have three lenses that it could fit. Plus with adapters, I can get my smaller lenses to work as well.
The filter. Overall its great. Metal construction with a very smooth ring.
The stops are marked on the ring and the overall construction is very good.
Again this is my first variable ND and so far I'm enjoying it very much.
Price is affordable too.

I love this 77mm ND filter that fits perfectly with my Nikon 70-200 f2.8. I use step-up rings for other lenses like my 85mm f1.4. The ease of use is phenomenal and it glides so effortlessly. I love this filter. I would recommend it to anyone to push it down to the darkest, open the aperture wide and take a long exposure during the day for amazing results. Enjoy!

The K&F Concept ND Filter does not have a stop, it will continue to spin all the way around. Though it does spin freely, taking the camer in and out of a bag/case may change the filter intensity. Otherwise it allows for much lower f stop. I use this while filming outdoor shots.

I have an ND 400 that I use for waterfalls etc but do not always want to block that much light so was looking for something a little faster Maybe an ND16.I have had variable filters in the past but have never been happy the dreaded Xs on the screen when you rotate or uneven colour cast across the screen.I saw the K&F advertised claiming that you did not get any of thease issues so thought I would try and they are great, very even light reduction across the frame and no Xs.I have the 77mm filter it is really well made there are stops on the rotation so it it easy to tell where the limits are, the frame itself is slightly larger that the 77mm so no chance of vignetting in the corners, the slight disadvantage of this is I can not seem to fit the filter with my hood in place but not a huge deal.Highly recommended.

This K&F Concept variable ND filter is to product that does not disappoint the photoamateur and based on the price paid, the top rating is fully earned. Needless to say, it is not comparable to high-end ND filters.
The only weakness, as pointed out in other reviews, is that it has no start and end point, so the dial spins endlessly. However, the problem does not exist for landscape shots where you have plenty of time to check the correct filter setting.
Vignetting appears only below 24mm, instead the cross only at the last stop in precarious lighting conditions. Colors are vibrant and not altered, color dominance is minor and for the perfectionists it can be resolved in raw in post production.
The following photos were taken with the highest stop, only the night one was taken with lower stops.

Qualities:
- very good materials
- very good finish
- perfect threading
- colors are vivid
- color dominance is minor
- top cost/performance ratio

Flaws:
- it does not have end stops
- vignette under 24mm
- cross only at the 'last stop with precarious light

Rated, based on price, 100/100