Started with two of them. I've been amazed how well they do in coldwater, and even poorly maintained tanks... I've kept them in all sorts of conditions and they've taken it all. Ravenous little guys too. Very not shy as well, they'll climb right onto you and pick your cuticles. Get along with just about everything and they even eat all variety of live snails, keeping them in check better than I've ever seen any assassin snail do.
Always wondered why they weren't bigger in the hobby in the states. I'm pretty sure they're pretty popuar in Germany and thereabouts, which is where they were discovered.