I've had a good play with a Xiosynth and they're VERY good fun. It's the portability... they feel like you could work on ideas on the train to a rehearsal using battery power, then plug in and go when you get there. It's actually not THAT hard to program them, the most obvious controls (filter cutoff etc) are mapped to the knobs on the front.
The distortion in the synth is pretty good too, it's much more... gravelly? gritty? than the distortion on my old Supernova. And... well, they're cheap enough that you don't mind turning them into a keytar
