I met some Teisco folks at a pedal/synth conference (before the world ended) and played their fuzz. I asked what it was based on, and the guys said it was a unique circuit. I have to admit it sounded unique and awesome!
Late to the party here but I used to have one and believe it's based on the Foxx Tone Machine! I've heard that repeated elsewhere. Great pedal, loud as hell, almost to the point of being unusable for me