I owned an RB for a while and I loved the Mamiya glass. The only MF glass that sucks is bronica's tamron glass. Junk. Pure junk. Even though I love Mamiya glass, once I got the Hassy, I quickly changed my likings to the Zeiss more. I'm gonna get some Zeiss sunglasses this summer. The coating (it's T*, but named differently) is on the inside of the lenses...weird. A friend of mine that has a pair was telling me that he could see distortion on the windshield of his car with them when the sun was at the right angle. So, I tried them on and sure enough, I could see a wave like appearance from the polarization of the glasses. Much better than any other sunglasses I've ever had. But, for the price of the sunglasses, I could get another body...
Printing the RB negs meant that contrast filtration varied between 1.5 and 3. Even on studio shots. With the Zeiss glass, I can print at 2 or use no filter all the time and I get shots which show a full tonal scale with no headaches.
The thing I never understood was why a Nikon LC37 (or whatever the UV filter is called) is more expensive than a Heliopan KR1.5...oh, wait...it's called marketing. I know a couple of Nikon users who frown on Schott glass, calling it "as cheap as the tiffen filters". Hmmm...can we say, brainwashed by advertising?