I bought a bristletail filefish to help with an aiptasia infestation. She's been very effective in that regard, I haven't seen any aiptasia in my tank in some time.
She does nip at certain corals, especially my birdsnest, but it seems to be big enough that she isn't harming it. She's also harassed my zoas and a rock anemone, but she seems to have tired of that and they are making a comeback.
She will readily eat PE mysis and Rod's frozen food. As others have noted above, she's definitely not the most aggressive eater, but she seems fat and healthy so she must be getting enough to eat.
Overall, a cool fish that happens to serve a very useful purpose in my tank.