User blog comment:XAero/UMP or P90?/@comment-1906486-20120523040554

I find their generally balanced.. and UMP can be upgraded to 50 rounds, just it's not common practice. 35/105 ammo makes it pretty decent. You can get quite a few clips used, before you go dry on ammo. Also it's not as fast of a firing speed, keeping it a stable control I find also it's rare to see.

Most people pick the P90/P90TR for it's quick spray and pray ability, 50/50 ammo and just general havoc it causes. Also the portability differences make a play on how you use it, since you might want something light to rush with. UMP's weight won't exactly help out, so a pistol / knife would be your aid there.