The basic idea is that it has
a) 5 special effect buttons
b) A bunch of chord buttons
c) A polyphonic keyboard of a few octaves
The music is recorded optically, in the way that film used to be until it wasn't. This means you can have all sorts of weird sounds. The downside is that things are at a fixed tempo, unless you slow it down or speed it up which changes the pitch. Hmm.
Well, the best demonstration is probably the TV commercial https://www.youtube.com/watch?v=MY4hyWds6Qk
There are lots of videos demonstrating it e.g. https://www.youtube.com/watch?v=dO8PRTcfO6E
This is allegedly a recording from the master tapes https://www.youtube.com/watch?v=ZPO9uXPFRRQ it includes the singing voices one 'Singing Rhythm' which I think were the best thing about it. Including the special effects for that one it starts at about 39 seconds
Have people made their own new disks for them? Of course they have. Radioactivox! https://www.youtube.com/watch?v=apna8Fhb0yE
And a minimalist one https://www.youtube.com/watch?v=x54Kc9062Xo
And a Drive-In intermission film with music done on an Optigan https://www.youtube.com/watch?v=KfLdGZvAEd4
So, do I regret not keeping it? Sort of, but probably if I had had it I would have given it to someone else. It has a degree of quirkiness but I'm not sure it was actually that good.