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.
lol it is only 100 ghash, Get the S3 over that since you can buy them cheap and used, they do decent undervolted.
If you are only mining for giggles the difference between 100watts and 400 is massive.
Although yes it's only $150 for an S3 which is pretty aweosme.
Well even for giggles it gives you a chance at more experience with more standard miner styles and there are more guides for them. If you want to learn to overclock or underclock there is TONS of information on the Antminer series and you can really get in first hand this way. Also yes you're right about the wattage but again if it is a huge concern it can be a big teaching lesson on tuning the miner down and increasing the efficiency.