Some Texas MACs had frame weld problems and would come apart, some violently.
IMO M11/9s are a crapshoot - some are great out of the box, others need tweaking, and still others need more tweaking. And I've seen M11/9s NIB for under $1000 recently.
Going through all the money and wait time you do for an NFA weapon, getting a junky one for your first gun can sour you on the whole process.
Have you seen these :
http://www.tacticalinc.com/mc/mcswd45w9-4.html
Craig has a great reputation on the boards, too.
If you're not getting a Powder Springs MAC, get one of his.
Good luck.