Cespitularia is not the cheapest coral and is sought after by hobbyist. I wouldn't worry about it spreading. Get the correct identification. Difficult to tell what yours actually is.
Picked it up from LA divers den. Looks like it when compared to other pics I have seen. I think most out there that say it spreads fast mistake it for pumping Xenia or Anthelia.
Apparently this coral tastes good to tangs. Yellow tang and hippo tang keep grazing on it. Angels have no interest but tangs....who would have thought?