MOST exotic loads work best in movies and on TV. Fire off a round of Dragon's Breath here in South Texas right now and you'd likely burn down a county or two. If you use something in self defense you might have to explain to a Civil Jury why you shot that poor defenseless child with something different than the Police use.
Many exotic and novelty loads don't have enough umph to cycle a semiauto shotgun.
Limiting factors include the excessive price and limited effectiveness of such novelty rounds. If they actually worked well, they would see widespread use and would be readily available.
BTW, there's a good reason the military stopped using most exotic shot shells, they don't really work that well specially given what you pay for'm. I've shot folks with buckshot and it works just fine.