I've heard good things about it. I'm sure there's some reviews kicking around here if you look for them. Batteries typically last one half to one shot per MAH. So 1000 MAH can be between 500-1000 shots, in my experience at least. I'm sure there's some variables that affect it. Only problem I foresee for you is mag storage. You'll need special P90/UMP mag pouches to hold your mags properly, but they can be found at a variety of prices. Try AirsoftGI, I think OE Tech makes UMP mag pouches, and they can be found there.
Not for glory, nor riches, nor honours, but for freedom alone, which no good man gives up except with his life.