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

The filter works very well on my Sony Alpha 7 III with a Tamron 24mm F / 2.8. There is no cross formation or other unsightly effects. The workmanship feels good and comes in a practical plastic case. As always, the shipping was great with Amazon. I can definitely recommend the 67mm version of the filter. BUT, the filter may not take into account that well in other sizes.

I bought this adapter to put a Ricoh 50mm 1.4 XR Rikenon in my Sony A7III, connected it to the first one, turned on the camera and it worked straight away

Works perfectly. The focus range is like the old SLR. The Ricoh lens creates a nice look with the S1R thanks to the adapter. Criticism: you could have installed a rubber seal towards the camera, but at this price I'd like to turn a blind eye.

It is a manual lens adapter.

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 :-)