The origins. Tone Bender MKIII, Tone Bender MKIV. Same party different frock. Aside from the obvious differences in the enclosure type of these pedals any true solid definition of which is what in regards to circuit type is and will always be a little bit of an ambiguous subject. The way I always made sense of it in my head was in regards to the biasing. The early MKIII's were choppy, heavy, clumsy, a fuzzy lump hammer. The later MKIV's were smooth, dynamic, articulate, a distorted boxing glove. In between, you have a foggy transitional period. Even with the those definitions in place it never always runs true.
Couldn't find a video of an original, so I figure the best example of the pedal is going to be the DAM version. Want to be clear, this layout is for an original Tonebender MKIV not the DAM one as travis pointed out.