Installed it today and it seems to be working beautifully. Setup was a breeze, especially since I didn't have to deal with the IR blaster. I just installed the Hauppauge WMC application, told it which inputs I was using and the path and arguments for firestb, and it was ready to go. TV setup in WMC picked it up as a digital cable tuner and set up the guide perfectly.
Channel changes still aren't as fast as my SD digital cable, but they're faster than the external HD-PVR was, taking about 3-4 seconds, and it seems stable. All in all I'm very happy, it seems like a simple and stable HD cable solution for WMC.