That's what pisses these people off.
Keep in mind the other stuff I posted about installation and non apparent problems.
Something made the U-Joint break. I'm assuming it was a joint in the car when you bought it so you don't know it's history. The previous owner may have had a thing for side stepping hte clutch or otherwise beating the crap out of the drivetrain.
On the other hand, a common problem with the T5 installation, far as I have seen reported by others, is vibration. And this goes back quite a ways, years. Vibration kills alot of componants.
The short of this is, I would have power train alignment checked. Not just vertically but laterally. And if you think it was difficult to find a shop to do a trans installation wait till you try finding a shop to do power train alignments.