They are really neat. I had one for about an hour. It was way smaller than the site I ordered from claimed and it became food. The only place i've ever seen them for sale was on azgardens.com, which is where I got mine. I would recommend never ordering anything from there. If you do a search here for that company you'll find all kinds of complaints.
If I could find someplace else that carries them, I would probably have bought more by now.
They dart around like a hummingbird (obviously), and I would love to see a school of them darting about.