The filters are stable and well made, have no problems with them.

I simply copied the complete text from my YouTube video for you. Who wants to see the video
"Variable Nano X Slim ND Filter I pure waste of money when buying?" Enter on YouTube...It's ND Filter that's hard to beat for value for money. It's about a filter from the company K&F Concept, this manufacturer's name is actually familiar to everyone who is - a bit - at home in the photo and film segment. And K&F Concept also stands for quality.
It's about the filter called NANO X Slim Filter. It is offered from a 37mm thread and goes up to a 86mm thread. Thus, it covers almost all offered lenses. He weighs just --- 45gr.
He has a total of 5 f-stops, it starts at ND2, 4, 8, 16 and ND32.
The filter comes with a nice round packaging as a transport box, so that it can also be safely stowed in a backpack or bag. But what is most important, especially for those who always leave the filter on the lens ---like me--- is the fact that glass is the filter's scratch resistant.
Screwing it on and off is wonderfully easy. If you buy it, you should definitely note that you can then usually no longer use your lens hood. Because the thread size on the front lens changes. Attention, however, when buying sun visors - it is essential to pay attention to the zoom range in which the lens is and accordingly buy a sun visor. Of course, I also had to buy a new sun visor, which I bought first was from 24mm, not intended for wide angle. My lens was 17mm – 28mm though. When I was completely in the zoon out, on 17mm, I had nice black edges in the picture. --- Stupid beginner mistake stop. So be sure to pay attention to the zoom area covered by the sun visor before you buy, just as a little tip.
The ND filter can be set very easily to the different ND levels and the individual levels are very well marked, so that you always know exactly which level you are at. Changing the ND levels is so easy because the filter is slightly corrugated all around and has a small pleasant resistance when turning.
In some recessions I've seen that some say the filters would appear to produce X-patterns at high f-stops. What I can't confirm with my film work at first. There is a spin stop, and no overlap, when setting ND16 to ND32, so the X doesn't actually show up. I only have the filter for filming, I'm a videographer, not a photographer, and I think it does a great job. A photographer and a full professional filmmaker will probably not use a variable ND filter anyway. I film a lot at f1.4, f2.0 and 2.8 and shutter 1/50 and even there, although everything is very open glare, the filter comes through perfectly, and very well with. Unfortunately, and that would actually be the only thing you could complain about, is that the filter has no IR cut. In plain language, --- IR, --- means infrared blocking filter. This blocking filter blocks wavelengths in the infrared range. What this filter does not have. But at the price?? somehow also understandable.
What does an ND filter actually do? ...
If some should ask themselves that.
Quickly and roughly explained ---- little basic knowledge.
First and foremost, an ND filter reduces the incidence of light and so you can still film in very bright situations, for example. Without totally overexposing the recordings. So also a longer eg. shutter speed possible. Who doesn't know the great pictures of streams or waterfalls, where the water looks like a veil, like in a dream world. You get that with a good ND filter and exposure time, for example, and not, as some people think or suspect, with good Photoshop skills.
I work a lot on the water, on the beach, on the sea, and that's how I always get the water nice and smooth.

Certainly not professional equipment but it is enough for beginners to try it out. You are somewhat restricted, as the transition is always in the middle and you have no way of shifting it yourself. But as I said for beginners completely ok. The bag that comes with it is also very useful.

Great ND filter with a great case. It works like a charm.

Unscrewing the filters creates great effects on the images.
I can recommend the filters, because you should experiment a bit with them.
For me this was a good buy because I would do it again.

I chose the ND filter with a 77mm pitch to be able to use it with my Nikon lenses and possibly use adapter rings for smaller increments. Well packaged and easy to use. Easily correctable with slight dominants in post production. Very precise packaging that allows you to take it with you in total safety. Equipped with a Frantal ring with the various corrections indicated. Switching from one tier to another is easy and smooth. It can be used in both photography and video and easily achieves good results. We recommend buying specifically for value for money. Ideal for landscape photos and always to have with you.

Wow! What can I say. Everything from the packaging to the filter is of such good quality. I have it on my Sony 16-35 and I haven't seen any vignetting or weird fading. I am really impressed.

After purchasing the ND2-32, I tested it for photography and videography. It arrived quickly in a quality case so is well protected. The ring works very smoothly and without problems. I got great long exposure shots without a vignette. For this price I can only recommend it to every photographer and filmmaker.

I received this variable ND filter today and immediately took photos with my Sony A7 III and the 24-105mm f/4.0 lens. I exposed manually and deactivated the live view display. The results were VERY convincing. This combination will soon also be used for video filming.

I had had very bad experiences with another variable filter a few years ago because it created colored streaks in the photos, so I had to return it.

Bought as a gift, she loves them.