Greenies? good or bad? for doggy bday party?

i made little treat bags for my dog's bday party (funny, i know) and someone suggested i put a greenie in everyone's bags. so, there, i did it. i blew $15 on a pack and now...as they sit in the goodie bags with other "safer" things (wellness jerky, old mother hubbard baked treats, lamb lungs, etc)...i wonder....should i explain to my guests to watch their dog with it or what? we have never used them before so i am clueless about the negatives and the positives. not a clue why i bought them. what a gimmick, no?