It’s called the giggle switch for a reason. While impractical most of the time, full auto mag dumps are simply VERY fun.
Yes, the 9mm Belt Fed AR-15 is real and is for sale. It is the Freedom Ordinance FM-9 and it is awesome. While us mere civilians can’t get the full auto version, a semi automatic 9mm AR-15 can still be a ton of fun on its own.