After running it about 20 hours I have nothing to complain about the U3 so far. I will keep it underclocked because it seems to run quite stable that way. And it doesn't matter anyway 50 Gh/s or 67 Gh/s is way too little in any case these days.
Where did you pick up a U3? I'm looking around... I'd like to pay bitcoin.
I have 7 brand new I just got in. Can sell for BTC assuming you are in US.