I have an umarex-licensed mp7 marui clone that I use instead of my socom on occasion. Both are bulky guns, so there's not much of a weight discrepancy between the two, also it shares the same type of mag release as the USP. The battery is small, but when used as a backup I never have any trouble with endurance. Plus the short mags hold 50 rounds and fit perfectly into the pistol mag pouches you already have. I've had it since 2008 and haven't had any issue with it, can't tell if I'm just lucky or what :P You can grab a left or right handed leg holster for it as well. Hope this helps
