Well, they can be pretty...but
IME, they are a lot easier to kill than Aiptasia. They also do not retract as effectively and are less likely to hide their base in a rock crevice as Aiptasia which makes them easier to kill. They also do not have a really small phase like Aiptasia, which makes it easier to find them if you want to kill them.
All that said, they can proliferate quickly, particularly if you feed a lot. They can sting other corals, and they tend to be much more motile than Aiptasia. They will sometimes 'jump' off a rock. I also do not know of a natural control organism that is otherwise reef safe. I'd be willing to bet that many forms of butterfly fish would eat them, but those same butterflies would likely snack on other corals.