I got a very small rbta like half dollar so far so good hasnt moved more than a couple inches either direction for ra few months now. Doubled in size since i got it. Made a rock with a Decent hole to set it's foot. Placed it between a lobo and a big pectinia. My clown which were hosted by the pectinia immediately took to the nem and now go back and forth between them. My tank is pretty full with corals in the hundreds. Right or wrong, just my experience.
Edit to add that it left the rock I made within a week, but hasn't moved much. And it touched both the lobo and pectinia but I don't think the nem liked it anymore than the corals did. All are well for now.