Ive been stung by these on the leg numerous occasions while diving and especially at night when glow diving as they don't have bio florescent properties like the corals they live around.
I've opened them up and fed them to the large blue groupers in Sydney that follow us everywhere like puppies.
Ive yet to taste one one though and maybe liken it to eating oysters. I will give it a go one day. Need my revenge on all the times they got me.