They are neat critters. Untill they're everywhere. But they do add motion to the tank. Do those pluse at all? I had some that looked similar and they just blew around in the current. A year or so later I was doing a w/c and saw them pulsing. After that night they never did it again. So I went and bought a pulsing xenia.....that thing flapped like it was flying south for the winter. Fun to watch. I think I got some vids of them. I'll see if I can dig them up.