I tried a baby Clown Trigger in my reef (105 gallon). When I bought him, he was the size of a half dollar coin. Other than eating a few of the snails and crabs, which I knew he would do, he was easy going. He didn't mess with the corals, polyps or my pistol shrimp/ watchman goby pair.
I traded him him when he hit four inches of so, but that was because I was down sizing my tank. Would I do it again? Sure. In fact, I have been playing the crazy idea of putting a small Undulated in my 90 zoa tank....
-avp