Used H3/4D backs with Arca and Alpa bodies for a while. Works OK and the battery was a non-issue for me when tethered. For extended sessions I power my phase gear with the same batteries I used for the Blad. However, the Blad really needs to be tethered while the IQ back, not so much. No way I could use the Blad back display well enough to handle focus, especially with movements. With the IQ back, I tether less because the display is so much better.
A fewthings about the Blad stick in my mind. For me, Phocus was a nightmare. On my equipment it was very unstable and I would sometimes spend an hour just getting the bugs out before shooting. Various FW driver issues, computer incompatibilities, etc. My PCs are pretty bleeding edge so maybe that's a factor. Lots of people don't have these types of problems.
If you need focus stacking with a remote camera, and are using the Blad body, the motorized lens is great. I could have the Blad ten feet in the air pointed into a set and make precise focus adjustments while sitting at the computer. Sometimes I would give up using the tech camera just to get this automation going. I REALLY miss that with the P1 system. In some ways - lack of camera control in particular - the P1/C1 system is very primitive.
Finally, I was blown away by MS. Those images really rang my bell and I would almost (only almost) give up the IQ for them.