If you are still looking for an MP5 semi, check the POF pistol version at Atlantic Firearms, the sell for around 1500, you can always SBR it down the road because the will accept a stock.
^ This
I had one of the older Auto Ordnance semi auto's and it was a really good gun. I never had any experience with drum mags in it though, but the stick mags that came with it, ran flawlessly.
I also own an sbr mp5k.
The MP5 is much easier and more fun to shoot if comparing apples. And weighs about half as the Tommy.
If I were going into combat with either/or, I'd go with the tommy due strictly to the 45acp caliber.
Unless you're planning on throwing a suppressor on the MP5 and running subsonic ammo. That would be more my style. (peak and sneak).
With that said, there are much more economical choices out there that would accomplish the same thing.
Hi point makes both 9mm and 45 acp carbines at a 1/3rd of the price or less as your first two choices.
Beretta has nice 40 and 9mm carbines for about half the price.
There are a few semi auto Uzi 9mm's being made at 1/2 to 3/4 the price depending on brand. And the IMI mini uzi pro pistol is also due out soon.
And don't forget that you can get an AR15 in standard 5.56 and a 9mm or 10mm or 40 S&W conversion upper kits for about the cost of the Tommy.
Choices are good.
I'm not trying to persuade you to get something different than you want. I respect that you have good taste in fine weapons. But I would offer the same advice to my sons.