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.
Don't bother with the new r-box. I have two (was only running one for about 5 weeks), one crapped out with in 2 months. Windows insists I'm trying to connect a USB 2.0 device to a USB 3.0 port even though it's plugged into a USB 2.0 port. I've had this with other USB miners too. I've moved them to other computers and everything, no difference... they're basically bricked. My other one is running fine (for now). I've only had this one going for about 3 weeks.