These are so easy to use and the quality is fantastic - both the build quality and the picture quality. I can't see any colour cast whatsoever from both the CPL & ND filter. I think you would really need to pixel peep to see any sharpness difference, and even then I'm not sure there is.
Being able to attach the filters to both the UV filter and filter ring is really clever - I keep the UV on my 24-70 F4 and the filter thread ring on 16-35 F4 so it makes it even faster to clip on the filters no matter what lens I use.
Since the ND isn't variable, there's no dark X. And no vignetting at 16mm, unlike when I use my square filter set.

The downsides that I see at the moment:
- You can't replace the filter thread on its own, so if you break or lose it, you have to buy a new set. I contacted support but was asked to pay $16 for delivery of a new thread....
- The range of NDs isn't as big as a square filter system (yet) and again I'm not sure if you can buy them as singles or whether it's just part of these kits

I had been wanting to try a magnetic filter system for a while so I'm glad I got my hands on these. All the magnets work well and it's easy to screw on the adapter onto your lens. I personally only really use the ND filter, but the other 2 filters could stack on no problem and without any degrading in image quality or color.

I was able to look closely at high resolution RAW files of photos I took using the ND filter and they looked extremely clean. The little carrying case is a nice touch as well.

One suggestion is maybe adding a 6 stop ND filter to the set. There were a couple times where the 10 stop was just a little too much light blocking for me.

I would definitely recommend this to most photographers as a great and easy all around filter system

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 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.

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.

Works great. 58mm I screwed ND filters on it. First the reflection from the water with the polarizing filter and then the ND filter screwed on.

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

This is the first variable ND filter I have brought and it does the job. Seems well made, and means I can use a lower F stop. The only issue is it does have a bit of an warm tone to the filter which you can easily correct by lowering the temperature in post. For this price I was expecting some colour shift so I’m happy with it.