So I take it that you won't be getting me one for my birthday, Cpt?
Way to burst my bubble.
Aside from any practical use in combat - which is very unlikely for the reasons you stated and then some (I prefer stealth, mobility and speed), I think it could come in handy against a zombie horde.
Think of it, the solanum virus spreads like wildfire so a person would need a butt load of ammo. Lugging all the ammo around on the run will get tiring/cumbersome. Being able to carry an additional 200lbs of ammo on the run seems like a bonus.
Or you could get dozens of these units and outfit them to monkeys and make them lug your gear. Just a thought.