They are beyond invasive and nearly impossible to get rid of. The will be aggressive (sting) other desirable corals and continue to multiply. Think of it as wisteria... once established it does not let go and strangles everything out. Also like wisteria, people sell them to unsuspecting folks
use a syringe and literally inject it onto the nem's mouth. Using the commerical paste is a good deal better as it prevents budding. Predation would be useful via several anemone eaters, such as certain fish/shrimp species. Still, it is tough to get them all but predation often works the best ... when it works.