I have been wanting to try these for a long time now. They seem to be available pretty sporadically though. The biological supply house seems to be the only place to regularly get them. I just never actually pulled the trigger on setting up a system for them or buying them.
I cant really answer your question on whether they sound like dero worms or not, I just have no "real world" experience with them. From what i know, them swimming in the water column and staying at the surface does sound kind of odd to me too. But really, I dont know. But in all reality...who cares...???
Your fish love them, they are growing well on them, and by the sounds of it you have a self sustaining supply of them at this point. To me, thats the perfect combo. Call them whatever you want, but your fish are calling them "dinner". haha