Just for the record, the Alien Bees radio trigger has 8 channels. I just got mine this afternoon...anxious to use it tonight. Also, I'll add that it feels quite secure in the hotshoe. Wiggles just a tiny TINY bit, but I don't see any way it'd ever fall out. It's in there good. Some say it "wiggles side to side", but there's no room on any of my hotshoes for it to do so.
Edit: Just looked at the Impact...it also says that it's 150' range, but only line-of-sight. AB works through obstacles. Walls, people, etc. It still fired. Apparently, this Impact will not. It does look a tiny bit like there's something to tighten it to the hotshoe, but I can't be sure. On the bottom right side of the transmitter, it appears there's three tiny bumps barely visible, which could be part of a tightening ring, but I don't know. Like I said, though...the AB unit isn't going anywhere. As for the 16-channel vs. 8, how many people are going to be using your strobes other than you, or strobes in the same area as you? Many studios on your block?
Oh, and the AB unit is slightly cheaper. I think it cost me $86 shipped.