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!

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.

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.

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.

Finally found an ND filter which can be installed inside the Smallrig lightweight matte box 2660.
I did have to remove the holder frame to make it fit. This can be done by carefully pulling appart the frame sides with the lips. In doing so you can op out the filter while keeping the frame intact.
Filter quality seems to be ok and it comes with a very well designed holder with an extraction ribbon which avoids having to touch the surface of the filter when taking it out.

I bought it to mount Nikon F mount lenses on a Canon 5D Mark IV and III body and it fits perfectly with zero slack. As these are manual lenses, there is obviously no autofocus and the diaphragm is closed manually.

If they added a tab that closed and opened the diaphragm it would be 100% perfect.

WARNING: no electrical contact with the box, you cannot adjust the aperture of the canon lenses without the aperture ring