Jon, I'm working on converting my full setup from Girder 3 to Girder 4, and today I connected the USB-UIRT to Girder 4 for the very first time. No problems what so ever. Just thought you'd like to know that.
I will do extensive testing the following week, so if there's something wronge anywhere there's a good chance I'll find it. But for now learning, receiving and transmitting seems to work perfectly. Good work!