I can honestly say, using the amd64 version of both beta3 and beta4, I did not require an ir blaster as long as the components were in close proximity, same set of shelves side by side, it even blasted around the corner to my TV!!!!!
However, for whatever reason, the 32 bit versions of these the onboard blaster did not function, and I had to plug in a dual ir blaster dongle to get it to work. And last evening I added an additional head to my dual blaster (3 now) and the 32 bit version, does in fact work well with the dongle. I control an AV recevier, a Dish 522 receiver, and a Sirius satellite radio now, all form the same USB-UIRT. my blaster dongle is home made, with parts from a local radio shack.
The USB-UIRT is truely an amazing device.