that I got my 175 gallon at, has a beautiful 200 gallon reef display tank. He had 3 heni's in it and I asked him. He said he wished that he would never have put them in there as they are constantly eating his corals. He has been slowly trying to get them out of the tank without destroying the tank, he is down to one in it now......I believe him when he says they eat corals, he had some for sale and advised us against getting them.
I would also take the advice of an online seller, they do use the phrase "reef safe with caution" when it is questionable. Also, if they are devouring aiptasia, that is a good indicator that they will nibble other things as well ..I would think