I am a passionate landscape photographer as a hobby and have now switched from the screw filters to this rectangular filter system from K&F. The screw-in filters were all fine, but you don't have the option of attaching a graduated filter to the ND filter in order to achieve even nicer effects.
It is mounted on the lens using so-called adapter rings, which are included in the most common sizes for lenses.
After attaching the adapter ring to the lens, the filter holder is attached. This is secured by a small lever (spring-loaded) and later released again with this.
Now you can slide the filter plates into the filter holder. This lifts a bit severely but it should also hold and must not wobble.
It is also important to observe that the filter used is close to the lens so that no more light can penetrate between the filter and the lens, which could possibly ruin the recordings.
In terms of quality, the system makes a good impression considering the price. The only thing I noticed negatively is that the filter holder has some play after it is placed on the adapter ring and why there is no adapter ring for a 55mm filter diameter in the set, I also ask. 55mm is a common diameter for lenses.

I can highly recommend the K&F system for amateur photographers. The professionals will probably use filter holder systems from other manufacturers, but they also cost a lot more.