The company that advertises this full-auto stuff makes all sorts of claims, like no background check, free concealed weapons permit. They claim to be selling "reel guns", including desert eagle, M92, glock 17, AK47, Czech 9, UZI, M16, MP5 and others, for <$100. It also says .25 cal. Perhaps they are not firearms, but some kind of airguns? I always wondered what was going on there.
I heard of that hellfire stuff too. They say that while it techincally works, it is even harder to shoot accurately then real full-auto, so it's pretty worthless for defense, but might give you a little fun on the range.