Them dang thorns hurt and can cause infections if not properly cleaned. Yes it sparks bad when air is introduced to the burned part of the wood. I have not used it in the electric smokers, but do know of a few folks that have used it in a stick burner.
While not having any experience with mesquite, Hedge is one of the hottest woods that most folks burn in a enclosed heating stove in this part of the country.
Oh, don't know about the fruit being poisonous, unless squirrels are immune to it. They seem to love to eat the hedge balls.