I have a couple in my tank, never saw them behaving badly. I even bought a big one from Reef Cleaners...unfortunately it didn't make it...hard to ship apparently. The ones they sell they say do great at eating algae.
I ordered a (fuzzy) chiton from Reefcleaners as well. It didn't move for 2 days and I thought it was dead...but then it disappeared into hiding. Now I see it probably about once or twice a week at night.
They (or at least the sp I have) tend to pick an area of your tank and stay there...mine has done an AWESOME job of keeping the shelf rock where it resides clean, as that bare rock gets blasted by my MH all day.
A word on moving them...reefcleaners warned that they attach very well to rocks with their mouths, and that yanking them off wherever they are attached usually damages their tissue/mouth enough to kill them.