I would recommend Massad Ayoob's book The Truth About Self Protection There is an very good likelihood that the Defender will be going to court, even in a justifiable shooting.
Massad Ayoob has stated that every single case of a NFA weapon being used has gone to a Grand Jury at a minimum. How much money do you have set aside for legal defense funds?
Even if it's legal, well and good, once it hits the public venues that someone shot someone (no matter the circumstance) with a machine gun, the anti's will have a field day with it.
It's not just the public views it is the costs involved.
If I defend myself with a handgun or shotgun, there are multiple cases of that happening and depending on location I may not see the inside of a courtroom.
Defend yourself with a NFA item and you will see the inside of a courtroom. Granted if you were justified, you might get off, but at what cost? It will get very expensive very fast. I don't feel the need to give the D.A. anything extra to have to look into or defend myself against.
I will stick to what is proven. Handgun or Shotgun. Until there is more case law regarding this stuff I don't want that headache.
One thing to remember. There are a lot of gun owners that don't think NFA stuff is legal. Heck some of them don't think it should be legal for that matter. How many gun owners do you think you may get on your jury? Now look at what the public thinks about NFA stuff. Most have no idea that any of this stuff is legal and most don't think it should be. Everything they know, they know from Hollywood. Now remember how many of those people will be sitting on your jury. As stated before. that is one less hassle I would want to have to deal with.