Get the "new r-box" from rockminer.
Mine has been hasing with no issues for months.. The U3 seems like a good idea alas is sounds like it zombies a lot :S.
I have S3's and a r-box both are awesome. The R-box is cheap and only uses 100w which is nice.
r-box consume 50 watt only at 35 giga/hash, yeah it consumes a low amount, but so its hashrate, pretty useless
good only for experimenting, if you never mined anything