I don't understand why these things don't go for more money. THEY ARE AMAZING! They're huge and they hang on the wall so you don't need table space for them.
I have both color combinations myself. They light up and revolve. They're constantly changing and I think they're at least as cool as the Mathmos projectors (and it doesn't have to be dark for them to work).
They also come with an optional clear plastic stand which the above one doesn't seem to have (I lost mine and don't mind because I like it much better on the wall). The following one (different colors) has the stand.
I really think they're going to be a major collectible of the future and, again, I'm really confused why they go so cheap. They haven't been made in years!