>>3939574>multiple timesno
probably just water-repellent and transmission-enhancing coating
most filter companies have two series of cpls, an a affordable one (just the two filter pieces) and a decent one (proper coating, sometimes also better glass). always go for the decent one.
k+f is an intermediate quality brand, meaning that they're convinced enough of their product to put their name on it but of course the filters are only a fraction of the price you'd pay for a b+w or breakthrough cpl. if you can't spare the extra 50 to 80 bucks for one of their cpls, go and buy the k+f (you might as well get an amazon basic one judging from the reviews). but in any other case, i would recommend you to get a breakthrough x4 (first choice) or a b+w xs pro (second choice). they'll save you a lot of time with adjusting colors in post and have negligible nd effects.