One thing to keep in mind is that the perceived value of transferable weapons is all based upon availability. Depending on who wins the next election, who comes to greater power in Congress, who is elected to the Supreme Court, etc. that value of your NFA investment could go from high to non-existent or you could lose your investment if the forces that be decide to ban transferable NFA weapons. Probably won't happen, but since you are talking investment and not just shooting pleasure, this is something you have to weigh in your decision.
I would suggest going to a local range and renting one and shooting it before investing thousands of dollars. FWIW, I think that an MG would be much more fun and entertaining than an AOW, AOW's are cool and fun to look at but frankly, they are not that fun to shoot, they are loud, they kick a lot and have quite a concussion/blast from the short barrel. I think that they are a much more effective HD weapon than a machine gun but if you mainly want something to take to the range, the Mac will be much more fun. The .22 kit seems like an economical way to go full auto.
I have shot a Mac and I own an Uzi. FWIW also, Macs are generally considered a "bullet hose" although the slow fire uppers mitigate some of this, versus the Uzi carbine is easier to be accurate with, better (obviously) to shoot semi-auto with, etc. But a FA Uzi costs about twice of what a Mac costs.
Have you checked out the Mac board over at www.uzitalk.com
? If not, I would suggest talking with Mac owners over there, the Macs are popular and there are ton of mods for them. You just need to decide if it is the right MG for you.