IMO, you'd be better off getting the littlebox instead of a UA-5 for your application. You can't take advantage of the UA-5's digi-out with an M10, so you might as well go with the littlebox which is more compact & does not require an eternal battery. I love my littlebox.
Even if you only record loud stuff, I prefer a preamp to a box that provides the phantom power, but you might be OK recording loud stuff with an ART phantom II. Having a pre certainly gives you a lot more flexibility though.
By the way your M10 provides plug in power and does not provide phantom power.