"...doesn't include a Thunderbolt cable, and at £39, this isn't cheap."
Compared to the price of the unit itself, it's not a huge proportion of the price, and it's still in its early days. Firewire and USB both took a while to catch on too. Oddly enough, it took Apple to give both the push they needed.
At least those Thunderbolt cables cost £39 for a reason. They're active cables, not just a bunch of wires wrapped in plastic: there's a chip at each end too, and THAT is why the CPU activity monitor showed nary a blip.
Believe me, USB 3 sucks for professional video work: USB uses a lot more of your valuable CPU cycles—cycles I'd much rather were being put to making me money, not making up for a cheap consumer piece of tat's failings.