Yeah, with good magazines.
Mine uses Colt magazines which are very expensive (like $80). I bought this gun during the "ban) but the price of these magazines has not really come down much since the sunset of the ban. Colt (as usual) doesn't want these 9mm mags to fall into the hands of mere civilians. I have some submachine gun magazines (Argentina ?) that were advertised to work in it and they do, but not as well. They don't lock the bolt back after the last round but other than that, they function OK. Pro-Mag is now selling a plastic mag for the 9mm Colt that I bought from Dillon. I have not had good luck with so far but I haven't really spent a lot of time with them. FWIW, magazines are either 20 or 32 rounds.
If you are converting a standard AR15 to 9mm, you can take a different route and use Sten magazines which are like $2.00 each. Sten mags are also 32 rounds. I bought my gun before I knew about this: mine is a Colt factory 9mm marked on the receiver as a 9mm. The mag block is pinned into the reciever. Most conversions use a drop-in mag block, so converting mine to the cheaper magazines isn't really an attractive idea.
Now, since this is the internet, I have to add that I have only fired my gun on ranges and during a few jackrabbit hunts. I never tried it during something like the D-Day landing or the invasion of North Africa. But, for my uses it runs fine. I have only cleaned it once since I bought it about 4-5 years ago. It operates by blow back in 9mm and not direct impingement like the 5.56 AR15/M16. There is no gas block, gas tube etc. The bolt is also different from a 5.56 AR15: there is not a seperate bolt and bolt carrier, it is all one piece.
I did have a little trouble when I first got the suppressed upper (
http://www.lrmfirearms.com/pages/863787/index.htm ). It took me awhile to figure out that the upper came with a "ramped" bolt.
http://www.lrmfirearms.com/pages/866797/index.htm This was the source of malfunctions. I swapped out for my original bolt and it runs like a top. When using the suppressor, the gun gets extremly dirty with powder fouling (carbon ?). But, this doesn't seem to effect operation.
FWIW, I have fired the Colt SMG a few times and really wanted one. But, I have never seen a transferable one for sale and don't have any idea what one would cost. So, I bought the semi-auto and tried to make it look like the Colt SMG:
http://www.colt.com/mil/SMG.asp
Here is an interesting article on the Colt SMG that also applies to the semi-auto in terms of range etc.:
http://www.chucktaylorasaa.com/coltm635.html Chuck Taylor seems to love his. He claims to have used it under battlefield conditions and never had a malfunction. He claims 4" groups at 100 yards and claims he can keep all his rounds in the "A" zone of a silhouette at 200 yards.
This gun, with the 11.5" upper (the 10.5" real Colt uppers were like 3x what I paid for the 11.5" I ended up with) is one of the handiest and fun guns I have ever owned.
Of course, since that time, I have learned a lot and now realize that you could make yourself up a Colt SMG by buying an M16 registered receiver and adding a 10.5" barreled 9mm upper, 9mm hammer, and a mag block.
Also FWIW, I don't think a semi-auto MP5 is in the same league with the AR15in 9mm. I have never handled one, but I have handled quite a few select fire MP5s. IMO, the AR15 is the better platform. Right out of the box it has far better sights to begin with. However, since mine is a flat top, I have an Aimpoint ML3 on mine.