Like Gazwas, at first I was not quite sure what to make of these.
I'm primarily a Profoto AIR these days because I use full power sync at 1/1000 quite a bit with my Leica S ... from D4-2400R packs, a bunch of D1 AIRs, a 600B AIR Lithium kit, and recently added a B1 AIR with 2 batteries. So, the B2 AIR could fit nicely into that round up.
Although 250W/s seems a bit limiting (and it is), more power probably would have increased the size. That small size coupled with being 3X the power of a top speed-light and being much easier to modify, makes it attractive, even if the price isn't*.
Monos, including the B1 AIR, are tough to work with in studio when boomed high overhead ... I currently use my 600B with the pack attached to the stand for things like a hair light because the head is so small. I could see this B2 doing that sort of milder duty in studio.
However, this seems mostly designed for "run-and-gun" event work like weddings and mobile portrait assignments. While 80% of that work could be done with 250W/s (I've used the 400W/s Quadra stepped down to that level frequently), it will run out of juice when fighting the sun (I've had it happen often even with 600 W/s!).
I'm always fighting the sun ... I shoot in Michigan in Summer and Florida in Winter. Unfortunately, wedding shooters do not have much control over when formals/portraits are slotted into a schedule, and all to often it happens when the sun is at its highest/brightest/harshest ... worst.
Don't really care all that much about TTL or HSS, except it would be nice when used at-camera in place of a speed-light for TTL fill when used in tandem with a key off-camera light such as the B1 AIR. At-camera TTL is far more important to me to control fill when working in mobile situations.
The Sony A7R is a bitch to use with lighting outdoors because of the limiting 1/160 sync speed. Even at its lowest ISO you have to stop down too much to control bright background exposures. I'd kill for a FE 24-105 leaf-shutter lens!
- Marc
* The price is a bit steep considering that something like all this in mint condition would cost about the same as the two head B2 kit without any modifiers:
Elinchrom Quadra - fotografz