No, both meters are the same. Check the mamiya documentation and post it here if you can prove otherwise. They didn't change the meter. They are both averaging meters, but the area of averaging is fairly small, and varies in it's relationship to what the lens sees. However they are the same between both cameras.
I find the tab easy enough to turn, and no risk of breakage as there is with the II. If I had kept the II, I'd have gotten the brass replacement tab from the guy in Italy that makes them.