Type: Monophonic Analogue synthesizer
As you can see it comes from the same period and genre as the Roland SH-101 and Moog Prodigy. A very fat sounding synth with arpeggiator and a simple sequencer. It has a good modulation section, some say it's the best thing about the synth. It is remarkably stable in tune once it has warmed up after about 15 minutes. Shouldn't be a problem finding a Pro-One, it's one of the most common monosynths.
Liam has used this one in live sets. If you have got the Electronic Punks video you can spot this one easily.