I have the B+W Kaesemann CPL filter in several sizes, but not the slimline version. The slimline is not threaded on the front, preventing use of the lens cover. The slip-on cover provided slips off way too easily, and can be easily lost. The added cost of the Kaesemann seemed reasonable, and possible vignetting at wide-angle focal lengths with the standard thickness version has not been a problem for me.