Wilt & Frank: Apologies, apparently I didn't make myself very clear. Obviously the higher the transmission, the better. Similarly, all other things being equal then no filter is better than even the best purely in terms of transmission amounts. I was trying, apparently unsuccessfully, to point out that with all the other factors which have a bearing on overall transmission, a difference of 2% is inconsequential in reality and may simply add confusion. The moment you start quoting "the science bit", an astounding number of people turn off or simply run away screaming (metaphorically).
Yes, flare has a bearing on image quality - of course it does, schoolboy physics/optics. But we were talking about the amount of light passing through a filter rather than any of the myriad other factors. Again, my apologies for lack of clarity.
Wilt: Strange that you should happen to drop on the Tiffen range as exemplifying less than ideal quality. They may have/have had a deserved reputation in the movie industry but the few I've seen for stills use have been pretty mediocre specimens. Perhaps it's the very tight control of lighting in the movie industry which makes the difference - or our comparitive lack of control! Another (European) brand which I've found to be rather over-hyped is Heliopan - very pricey indeed for what you get. Not actually bad filters, just way over-priced and often bettered at a lower price. I also never found Rodenstock particularly good value for money though it's about 20 years since I last looked, they're nowhere near as commonly found as once they were. (But I do like my Rodenstock Softar II, the one marked "Carl Zeiss Germany" .)
Frank: You're quite right about Marumi's phraseology. I hadn't looked at that site at all, now I come to check it's also repeated in form/substance on Kenro's (UK distributor's) site. I too would expect them to conform to the norm of ultra-descriptive terminology yet they seem almost reticent. I wonder if it's mere etymology, refering more to the fact that there is coating and less to the configuration. Whichever, I was assured by Kenro MD when the DHG Super was first introduced that it referred to a multiple layer, vacuum-deposited coating with particular attention to the rear surface which is the one which would produce internal reflections and non-imageforming flare.
Similarly, I can't find any reference to glass homogeneity, surface smoothness or plano-parallelism which are equally important in producing quality optics. Hoya, too, are pulling back on the availability of technical data - is this a trend or is it just industrial secrecy? Once upon a time, I had a legitimate hook on which to hang some investigation of this but no longer - despite the curiosity still being there. I'm just glad I'm not in the market for any more gear these days.