Phil,
You say you are considering the Credo 50. I've had it in the studio for a few days (on a P3) to test and on the strength of the results I ordered one on Monday.
It works well with USB3 and I was quite amazed at how quickly the pictures come into Capture One! Picture quality is good too, as well as tethered Live View on the monitor and I will be using it initially with my P2 and a few Rodenstock lenses which I am having converted to the Sinar e-shutter, which I find much nicer than my current Rollei Control-S.(but alas, extremely expensive).
I am using El Capitan with a new Mac Mini with SSD drive, plenty fast, it all works.
I didn't consider the Hass, because I wanted to shoot using Capture One and because I have had 2 Aptus 65's since the time they came out, about 9 years ago, and they have been superb, not a single problem and the Peartree guys and Yair here in London have always been helpful.
Anyway, I thought you'd like to hear some opinions.
(BTW, I have a Mamiya 645 that I've never used, other than to test it initially, it came with the Aptus as a package, and also have the Mamiya 120 Macro, all unused/mint, I am not really a medium format guy, I will sell these in the near future when I find the inclination to bother)
Edward