I was able to play Bill's purple people eater racked SLO at Jame's ampfest a few years ago.
In all honesty the SLO tone sounds dated. Loud mother fuckers, but they need to be cranked beyond 4 on the master volume to even begin to wake up. I think we were running his on 7 before the goods were given up.
The LP players there were loving it - rock city and had saturation with great touch response. But In all honesty I preferred James' Bogner Uberschall Rev2 or my own 5150 II to it.
They are great, but the tone is not worth the price. For $3k+ I'd prefer to look elsewhere.