I tested the K&F Concept filters on a Canon EOS 5D Mark III with a Canon lens.
I am very satisfied.

The filters are very well made. They are delivered well packaged. It is also practical that you get them right away in a well-padded bag and can thus store them well protected in the photo backpack. So the filters can also get no scratches and you always have the filters of one size together.

Also supplied is a cleaning brush.

The filters are absolutely accurate fit. This is not self-evident for filters of this price category.
I received the filters on a test basis which has no influence on my rating.

Original photos

Its perfect for my Canon EOS M6 mark II with the 22mm lens and the Canonb EOS RP with the 35mm lens ... I was amazed from the quality and the compact size ...

Got this for my "nifty fifty" Canon 50mm 1.2 L lens on my Canon 5D Mark IV, and they're pretty solid.
You get three filters: (1) ND4 (2) CPL and (3) MCUV which are all pretty useful in different scenarios.
A huge plus for the included case, soft brush, and price point.
Overall, I would recommend this for any creator doing photography BOTH indoors or outdoors, and looking to significantly reduce reflectivity!

I ordered this filter for my Canon M50 Mark II lens and it fits like a glove. The material of the filter is metal and robust. The coating on the lens ensures more realistic colors. I recommend it as an addition to your camera equipment.

This is a very nice high quality ND filter, as expected of K&F Concept. I'm using it with a Canon EOS 5D DSLR, and it is very fun to play with. I haven't used an ND filter like this before so I'm still learning, but you can definitely get some cool effects especially with moving water. The glass is high quality and the picture is sharp and clear. I have a couple of other K&F filters and this is just as nice to use as the others.

In perfect condition. I fit great with my Canon Mark II. The focus is on the hand

use the following other lenses on my Sony A7 Mark III: 24 - 105mm 4.0 | 16 - 35mm 4.0 | 85mm 1.8 | Just so you have references for my review...I think the lenses I listed above are beyond reproach. I was skeptical about the Samyang at first. I bought the lens because I ... a) wanted a light fixed focal length that forces me to use this really "cool" 35mm;-) b) wanted a light combination c) I'm still relatively flexible with it ("Street " not necessarily only people, but in the city) possibly also portraits (not classic, just more reportage) ... the fixed focal length should of course be quite sharp (but sharpness is really not the most important thing for me when taking photos, just a side note) d) Face detection and eye autofocus would be very nice because then I can focus on composition The Samyang really has all of those things. That's a really good lens! It is of course a value for money monster! The only downside... no metal, but plastic. But I can do without it. It would be "stupid" the other way around. Metal and for that a cucumber of lens, right? Here you can really access without hesitation. It's a lot of fun, the autofocus works really surprisingly well...I wasn't really expecting it.

I bought the K&F Concept ND filter for my Sony Alpha 7 III. I use the 67mm version.
The filter arrived the third day. Everything was well packed and undamaged.

The processing is really impressive. Very clean glass and no scratches or anything like that.
The intensity of the ND filter can be continuously adjusted from ND2 to ND400.
I took a few test photos with the filter and am absolutely satisfied.
The only drawback for which there is a star deduction: At the maximum filter level you have a bluish shimmering X in the photo. This is a bit annoying, but if you turn the intensity down to just below the MAX level, it disappears again.

All in all, you can't go wrong with the ND filter from K&F Concept. At a reasonable price you get a universal ND filter. I give it a clear buy recommendation and because of one shortcoming 4 stars.
I hope I could help :-)