I bought the rectangular filter set directly from K&F.
Since I have worked in the past with screw filters and when screwing several filters on top of each other got the problem with vignetting I wanted to buy a rectangular filter set for a long time.
Since the sets from NISI, Haida and other well-known manufacturers are very, very expensive, I was looking for a cheaper alternative as a hobby photographer.
When I saw several reviews on YouTube, I decided on the set from K&F which is half the price of Haida and CO.
I have not regretted my decision until now.

The filter holder is very high quality workmanship and well thought out.
I especially like how the polarizing filter is attached to the holder and how it can be adjusted via the small wheel.
The filters themselves are made of optical glass and show no color cast and are also well coated.
Also positive to highlight is that the filters are provided a plastic frame with a tab.
So the filters can be inserted and removed without annoying fingerprints.
Included is a bag to store and transport the holder and the filters in it.
Also included are several adapter rings for different filter thread diameters.
I as a landscape hobby photographer would not want to miss the advantages over screw filters.

From me there's a clear purchase recommendation for hobby photographers and professionals!!!
I would not have expected such excellent quality for this price.
Madness what K&F delivers here.