I have run an RPi with both U1 and U2 with bfgminer. I don't recall the bfgminer level. I always had the U1 and U2 on a solid powered hub (e.g. a 7 port Dlink with plenty of power). What I always did was after I booted the Rpi, but before I tried to run bfgminer, I would look for and count the /dev/ttyUSB* entries. There should be one for each U1/U2. That tells you if the Pi
has recognized them. I also recall having to build bfgminer with some specific argument to make sure it had the right driver, and recognition software included.

This may all be moot if you are happy with cgminer.

Regardless of the mining software, you will want the U1/U2 on a powered hub.