I've had two. One that I picked up from the LFS. Great success with the little guy and it cleared all form of aptasia. One day it went after a Xenia frag I introduced and so I returned it to the LFS. Everyone missed the guy because it had such a great personality and always up front when you walked by.
Second one is in my 210 gallon today. I ordered it from Pacific East Aquaculture since it is captive raised BIOTA. Like yours the size of a dime if that and didn't make it in my display no matter how much I tried. Sump was out of the equation since it is someone small and 3 pumps to navigate so I threw together a 5 gallon nano for about 2 months. I put in test rocks with aptasia and it would eat it without hesitation. So I knew that was going to work...
Today, 5 months later, nothing is really safe from this guy or gal. It took out two maxima's, duncan, zoas, and starting on my hammer coral now. Having said that it has left alone my rose bubble tip anenomes, montipora, cabbage coral, xenia, acan, and a few leathers. So I ask myself every day if this is acceptable to keep aptasia in check. So far I say yes because I know aptasia is in the plumbing and sump and a few rocks the fish doesn't get to. Berghia are too expensive in my opinion and I have not found a copperband that I like yet since the world pandemic.
So we are more or less at peace with one another and I take responsibility for the acceptable loss :D