If you are hearing bad things about ball anemones, my guess would be someone has misidentified their aptasia or majano as a ball anemone. Ball anemones are harmless filter feeders that are typically (not always) found in dark areas of the tank. Mine never seemed to impair any corals they were near.
They won't take off in an anemone specific tank without some specific care, and even then due to them being mostly clear, I wonder if the visual appeal would be worth the effort. If you see tanks that look like ball anemones, but are bright red or orange, those are a strawberry anemone type that are found in cold water (Oregon/Washington/N.Cal) and will not thrive without chillers and a dedicated NPS tank. Good luck.