Anthony, I'm using the 70MZ5, the biggest "hammerhead" from Metz; lots of power, but quite bulky to carry around. Mounting on the camera takes more time than a shoe mount would. It all depends on your work-style what will fit you best.
Digital: Please be aware that the glass filter of a digital back is less reflective than a film surface. This means that using TTL flash measurement will give over exposed images. My advise is to select a flash unit that can be used in Auto-mode, since then it's the flash (or its control unit) that's measuring the light reflected from the subject. The TTL flash correction on the H1 (+- 2EV?) is not enough to compensate. On a Kodak Proback 645H that I tested, overexposure was at least 3 EV in TTL mode.
My experience with studio heads and digital is limited, but I did experience that combining different heads was not so smart. The back is very sensitive to variations in colour temperatures, so combining some cold head's with others slightly warmer gave a visual variation on a white background.
I wouldn't count on less expensive medium backs for a while, though. Remember that making big CCD's are very expensive due to the failure rate on the disks they are produced on. When the size of the CCDs grow, the chance for one pixel to be corrupt increases, yielding a higher rejection rate than with those used in compact or 35mm DSLR systems. Until someone solves this problem, or the production cost of those disks drop significantly, I'm afraid that new backs will stay expensive for a while. But you could consider used, though. Since Kodak no longer produces their medium backs, I'm sure there is someone out there considering other alternatives. Some dealers might also sell their demo units for a favourable price.
