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
The new R-box is 110 Ghash at 110-120 watts.
http://shop.rockminer.com/goods.php?id=44Priced very well. I didn't even need a powersupply as my computer powersupply is solid so I juse used a spare PCI-E plug and run it from my comp powersupply using my comp as the controller.
.25 BTC for the miner plus shipping is a solid deal. I am tempted to get another one for fun.