I would rather have one of these http://www.amazon.com/New-Trent-Sensation-Thunderbolt-IMP120D/dp/B003ZBZ64Q/ref=sr_1_1?s=electronics&ie=UTF8&qid=1364951263&sr=1-1&keywords=imp120d. I have an older and smaller one and it works very well. Amazon has models in different sizes.
Batteries + sells a similar unit <$20 and it uses a couple of AA batteries.