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

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!

ordered the adapter to use a vintage Tamron mirror lens (5.6/350 mm) on my two Canon bodies EOS 5D mkIV and EOS 1Ds. Since both cameras are not listed in the compatibility list of the item description and one often hears (with other adapters) that the camera mirror can no longer move freely and therefore error messages or damage to the camera occur, I was curious whether that would also be the case my two cameras would work. It works out. The adapter is also seated without play, attaching and detaching is easy. It was clear to me beforehand that the focus and the time setting had to be made manually. Unfortunately, the invoice must first be requested from the seller, but it came within 24 hours as a PDF by email. However, it is an import invoice without deductible VAT and in the "worst case" the tax office will still have import sales tax when it is submitted. At the price of the adapter, however, that can probably be gotten over.

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

use the lens on my Canon 5d II full format camera - I am very satisfied with the imaging performance. Of course there is vignetting with an open aperture of 2.8 - but you hardly take pictures with it anyway. There are certainly better lenses - but you have to put down at least twice as much and therefore I can only recommend the lens to everyone who wants to use it from time to time. Anyone who needs a UWW professionally should take a look at the 11 or 15 mm from IRIX.

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.

Use this on my Sony A7 III and I'm thrilled. Darks really great without discoloration etc.

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 :-)