I've trained with the MP-5, MP-40, and UMP40. IMHO I much prefer the original. The MP-5 was originally designed to be a CQB and hostage rescue weapon. It was damned near perfect for it then and I think it still is. It's portable, reliable, and compact. It was never designed to take the place of the rifle or carbine. The .45 is a great cartridge but is not the answer at 100 yards anymore than the 9 or 40. If the bad guys are wearing body armor the 40 or 45 will do no better and in some cases worse than the 9. The idea is to put multiple rounds on target as quickly and accurately as possible. That is easier with the 9 than the 40 or 45. I did'nt like the UMP at all with the mickey mouse plastic sites, it did not impress me. Don't take this personally, it's just 1 persons opinion, but it's honest.