This is a cool module to make electronic sounds with. In case you want realistic imitations of acoustic instruments, look elsewhere!
This is a sound module that uses FM (Frequency Modulation) to produce sounds. This works by having several oscillators where some oscillator modulate the pitch of other ones. If the modulation is quick enough (i.e., more than an ordinary 'vibrato'), it gives rise to a very overtone-rich sound. Since every oscillator (called 'operator' in this context) has a separate envelope and can be controlled by e.g. aftertouch and/or pitch bend etc. individually, you can make really cool noises with this machine.
I have finally learned how to program it (it's quite tricky at first), but unfortunately I don't have much time, so I mostly re-use old sounds. I don't think I will sell it, since I like the sound so much and I won't get much for it anyway.