The size is around 3 inches range and the color is very beautiful in that tank compare to FO tanks. I do not see any immediate damage to his reef tank.
My LFS feel that his reef need "population control" so he put one in. The way I have seen and I do not see any IMMEDIATE threat to reef. I guess it have to depend on how well establish reef tank before consider such that decision.
Another thing I have see Raccon Butterflyfish in reef tank in Atlanta pet store. Same one for over a year.
According from the petstore that Pearl Scale, Raccoon, and Cooperband are reef safe (you have to monitor them careful before you put trust on them. individual differs.) compare to any other butterflyfish.
Good Luck.