Bought a Dr Blankenstein Illumiringer on Ebay recently and it arrived today. Still undecided where to install it, originally I was thinking a bass but now leaning toward a Speak and Spell. It allows you to control pitch via a knob or optical sensor but I'd guess it adds a lot of character too.
I'll post a demo when I'm decided. Only other comment until then is that Dr Blankenstein should quit smoking.