So I decided to give this system a shot. I purchased 2 Flex TT5 units to start with and see what I encountered.
I am using a 5DmkII with a flex TT5 as a transmitter. I use a 580exII with a flex TT5 as a receiver.
Distance: With the 580 on the TT5 I can only trigger reliably to roughly 30 feet inside or out.
If I push the TT5 out onto a flex arm with a cable, things change quick. Whether I used a ferrite choke or not didn't make much difference strangely. I even tried gaffers taping chokes onto the flash to see if it would do anything. Nothing much so far.
When the TT5 was about a foot away, I was able to trigger reliably to about 110 feet. Between 110 and 170 feet became somewhat hit or miss, especially if it wasn't line-of-sight. That's pretty darn far though. Honestly, I can't imagine needing anything beyond 50 - 70 feet.
High Speed Sync: Amazing! Works perfectly! At 5 - 10' feet from my subject I could sync at 1/8000 at f/22 at ISO 3200. So being back down to a reasonable f/4 or 5.6 with ISO 400 means I have some pretty amazing freedom with the speed setting.
I had no problem with any of the controls on the 5DmkII and the flash. I have not tried with the ST-E2 yet or a 580II on-camera to control ratios, so far so good. I'm going to order some more TT5 units and see how this goes with multiple flashes now that I see results that are good enough for my work. It would be nice not to have a flex arm attached, but I can live with that for now.
EDIT: I am using default settings on the PW except for the sync setting. Sync begins at 250. I use channels 2 or 20. Everything else is default.