That Polish testing site is great, Klaus; it answered longstanding questions for me. My takaway:
(1) The newer Hoya "Pro1 Digital MC" series is at least as good as the older "Super HMC." (Although, come to think about it, my Hoya filter packages are labeled "Super HMC Pro1," which I believe means that they have the same coatings as the "Super HMC" but are thinner for less likelihood of vignetting.)
(I had heard rumors that the newer Pro1 Digital MCs were not as good as the older "Super HMC" models.)
(2) The Kenko "Pro1 D" filters seem to have flare characteristics about equal to the Hoya Pro1 Digital MC, but are priced much lower in the US. Kenko and Hoya are owned by the same company, and I have read that these are "corporate twins." However, I note that the Polish review has some caveat at the bottom (unreadable by non Polish-fluent souls like me) that causes the scores to appear in red.
(3) The German B+W and Heliopan filters appear to be a very bad bargain for the money. Lots of extra cash for little or no additional benefit in flare and transmissivity characteristics. (However the frames are brass rather than aluminum.)
Anyway, these filter companies are very cryptic in their naming conventions and in the technical material on their websites. So, the Polish testing read was valuable for me.