I've been toying with the idea of ​​buying a gradient filter for a long time, although the prices from Nisi, Haida, etc., around 150 euros, have always put me off.
Then I came across the filters from K&F, because the filters were reasonably priced, I ordered them.
The extremely beautiful and high-quality packaging should also be emphasized. Here you get an imitation leather case that is lined with fine fabric on the inside and has 2 magnetic buttons incorporated. This case is again in a nice padded cardboard box, very valuable and stable so I wasn't really disappointed.

Filter holder:
First of all, it has to be said that you need a filter holder system for the filters, which costs around €25 at K&F. This is well made and serves its purpose. Here comes the filter holder in a padded cardboard box. The scope of delivery includes the filter holder and 8 adapters in the size 49mm - 82mm.

So I'm already looking forward to going out into nature with the filter to test it.
The adapter ring is screwed onto the lens thread and the holder is simply mounted on the ring with a snap mechanism. The mount holds securely and doesn't give me any concerns that it might not hold even with minimal play.
The optical quality of the gradient filter is great! I didn't notice any loss in image quality and there's no distortion or vignetting. Furthermore, I could not detect any color impairments or other color distortions. The filter does what it is supposed to do, it easily darkens an overexposed sky and saves me a lot of work in post-processing.

Conclusion
Since I haven't worked with ND filters before, I don't know what I could complain about here.
Overall, I am very satisfied with the glasses from K&F. You get a high-quality, processed filter with top optical quality and a good scope of delivery (artificial leather case). For the price of around €89, it doesn't need to hide behind the other brands. I will soon buy more glasses from K&F.