Among several domestic and foreign companies offering square filters, I decided on this one because it is easy to put on and take off from the lens, it is thin in the front and back, and it comes with a C-PL filter
For C-PL filters, just open the lid and drop in from above. If you make a mistake in front and back, it will not fit.
The square filter has just the right amount of friction and doesn't feel like it's going to fall off.
Almost all metal, except for the four metal adapter rings and C-PL filter, the holder alone weighs 110g.
In terms of design, the overall impression is sophisticated.

After many reviews that I looked at on Youtube, I decided on the new K&F filter holder and have not regretted it so far. It is easy to use and makes a very high-quality impression. The use of the CPL filter is a great solution. Lever up, put it in and lever down again, done. Adjusting the wheel is also buttery smooth. In contrast to the first K&F filter holder, the filters, which now have a frame, can now be pushed in very easily. Not too easy and not too heavy either. A clear buy recommendation.

Had screw-on filters for years. Of course they work, but a plug-in filter is really practical, especially for landscape photography. I first bought the filter plug-in system from K&F (Nano x per row). Now have some filters. Filter and plug-in system highly recommended. I'm really excited. Goes fast, good quality and you can also leave filters on if you want to go a few steps further. I also like the frame around the filter. That way, greasy fingers don't get on the filter so quickly. Nothing wobbles. There is also a stylish filter bag.

I was really looking forward to it, everything is packaged beautifully and with high quality, so you can't say anything really great

This is a very versatile system and a quality product. The tabbed filters slide in and out of the holder without difficulty. So far, no light leaks. I love the ability to get frames for my additional filters, 100X100 and 150X100. It keeps fingerprints off the filter.

The company is based out of Hong Kong. I would have liked to get additional adapter rings, but the company does not sell them separately, or so it seems. I've contacted them via their web site/email address and keep getting ads for their backpack. I was referred to get magnetic adapter rings which are not for this system. It appears if you want to get adapters you need to buy the filter holder and adapter rings.

This is definitely a product to purchase. I look forward to shooting pictures with it. It would be nice to have a wide angle lens shade, but then, you can't always get what you want.

Does what it's supposed to do... and very well made

Excellent value for money. Well though out, made and engineered, comes in a nice box, all very well presented. Complete with adaptor rings to fit most lenses. No colour cast that I can see. Im very pleased with the filter kit and have produced good images. Would recommend K&F Concept Pro Square filter set to anyone not prepared to pay silly money for other brands.

It's been a while since I hesitated between several brands to choose a filter holder for ND and GND filters. I took advantage of a flash sale to purchase this kit. I'm not disappointed. The whole thing seems sturdy and easy to store. The case, quite pretty, has 5 compartments, 3 of which, for square ND filters, can be lifted using a ribbon. On the back of the case, there is a ring for passing a strap and a belt loop. I would have liked a slightly more spacious compartment to accommodate the adapter rings with the CPL filter when it is disassembled. The assembly (or disassembly) of the elements is well explained in instructions in several languages, including French. Main positive points: No color cast, nor loss of sharpness on the first tests carried out. The plastic frame with its tabs for handling the ND filters. The system for placing the CPL filter on the filter holder. The knurled button for mounting the adapter ring and rotating the filter holder. The very accessible wheel to control the polarizing filter. The vigorous holding of the square filter on the filter holder. The robustness of the metal filter holder. If we have to find some slightly negative points: Holding the square filter a little too vigorously in the filter holder. The click too strong to lock the CPL filter in the filter holder. No pouch to independently protect the CPL filter in the case.No protective cover for the CPL when the assembly is installed on the lens.

Works great on my Nikon Z6 16-30

I haven’t had to use it at this point since I use a slow ISO film to begin with. Will use it in the future though I am sure.