The CPL filter from the K&F "Concept K-Series Pro" makes a reasonable impression. The filter, 82mm in my case, can be easily screwed in without any extra effort, thanks to the milled trapezoidal structure. The term "nano" is misleading in my opinion; I can't imagine that you can get a real nano coating for the relatively low price. Nano-coated filters are easier to clean, but streaks quickly form when cleaning. But that's just a guess. The filter is multi-coated, according to the description 18 layers, but that can't be verified either. But it is coated without question, which reduces the tendency to reflection and reduces ghosting in the final image. The filter disks rotate slightly against each other with the typical polarizing filter effect. AF works perfectly for me with the filter screwed on; I couldn't detect any exposure deviations, nor any color shifts or drops in contrast. Everything works perfectly. The same applies to the sharpness; I couldn't detect any significant influence of the filter. The filter is relatively light, which shows that little material is used. The lenses fit well into the frame without wobbling. The slim design means there is no vignetting and no drop in brightness in the image. It is therefore also recommended for strong wide angles. The complete scope of delivery is exemplary, including cap (snap-in), cord, cleaning cloth and plastic case. The snap-in is a bit loose on me and can be easily removed without pressing the lock, so it can easily be lost (so use the cord!). All in all (for cheap optics) it is worth buying. You can't go wrong with it. A higher quality filter should be used on a 2000 euro optic.