John,
Which did you decide to get the longhorn or the blue boxfish?
I have kept my cowfish in my reef for over a year now with no problems.
I have never had my cowfish nip at any corals. But who knows maybe there is some coral out there that I don’t have in my tank that might just be tasty to a cowfish. I have not encountered it yet. When they say boxfish are not reef safe I believe its because they will eat inverts. They will go after hermits, snail, scallops, clams, shrimp, etc, but usually not able to eat them until they get older due to their small mouth.
Every once in a while my cowfish will go after my shrimp but had never touched my cucumbers, sea hares, urchins, lobster. Cowfish have the ability to blow air in the water to uncover their prey. I have seen my cowfish do this with small hermit crabs or pods and eat them. Mine also seems to do this with my large pagoda coral but I discovered it was in search of food particles of uneaten food in the stony plate. My cowfish is always hungry.
I think cowfish are one of the most fascinating creatures in the hobby.
Congrads on your new cowfish!