If you only want PC, the DualStrike does keyboard encoding while the Cthulhu does not. To the best of my knowledge, the rest of the PC features are comparable if not identical. If the extra cost is worth the keyboard encoding feature, go with the DualStrike.
I can confirm it works well on Win 7. I just put a Dual Strike into a my stick a 2 weeks ago or so and it works just fine on Windows 7 (64bit). I did not have to update firmware or anything, just plug and play.