I use a Mac, but haven't successfully used the Mac beta connected to a camera - it had a bug that prevented it from working for me, that has supposedly been fixed, I just haven't needed to use it since then. But I've used it for manual mode on the Mac (where you shoot a set of images with different AFMA values, then load them into FoCal for analysis, and that's fine. I've also run the Win version on my Macs in both Parallels and VMWare virtual machines.
Be aware that with the 5DIII, fully automatic calibration isn't possible due to limitations in the Canon SDK. You need to manually change the AFMA setting.