They are hard to establish. In a bigger reef tank, they can be overcome by flow and have a hard time finding more aips to eat. Crabs can jack with them. The are pretty fragile. If they establish, then they can be really effective.
Even if you can get them to eat all of your aips, they will stave soon after. Right about then, then little ones that they could not find or eat will get large again. This is similar to people who sell copperbands right after they don't see any more aips... they nearly always come back.
Peppermints from the keys (confirm it before buying) will destroy aiptasia, although sometimes you might have to knock back some of the HUGE ones with some kalk before they tackle them. Peppermints from other parts of the gulf are hit or miss. They can also stay in your tank for long term control.