Hi Roger
The back and camera have just been sold, but to answer your questions. The back itself is not more reliable than a back for the Mamiya system, but the Hasselblad H system is (IMHO). The H system has been tested and proven and has been working for more than 10 years. The lenses do not hunt and the focus is right on. There are no connection errors, the firmware just works. That's more than what can be said about any other system out there today.
In regards to the Hasselblad 500 system. The lenses are not as sharp as the Hasselblad H lenses and keep in mind that many of them have been sitting untouched on a shelf for years. The sync timing might be accurate, it might not. Digital backs need a precise sync signal from the lens. In regards to autofocus, the camera can most likely focus quicker and more precise than what you can, but keep in mind that there is only 1 focus point which is located in the center.
Best,
Esben