I just got my ToneDexter this week. I ordered it before everything got locked down, with the full expectation of using it on some gigs right away, but now there's no great urgency in getting it dialed in since there are no gigs on the immediate horizon, and that horizon seems to be moving as I write this. Regardless, I thought I'd share my experiences so far.
My bass is a 3/4 sized Pfretzschner carved instrument, set up primarily for jazz, with Spirochore reds and a Full Circle.
I was able to easily download the bass-specific firmware (V 1.62) and load it into the unit.
Training went pretty easily, and I found the manual to be very useful without being overly complex.
Using slot 22, I used my Advanced Audio CM 67 large condenser mic aimed at the end of the fingerboard about 8" away, which is exactly how I record the bass in my home studio. On the first training pass I bowed almost all the way through, but on a subsequent pass I played pizz only and that seemed to produce a more balanced result (the arco pass had a bit of harsh high end for some reason). I tried another training pass with the mic halfway between the bridge and the treble side F hole, about 10" away and aiming slightly toward the bridge (with the same mic), which is how I've occasionally had success recording the bass for a rounder and deeper sound. The ToneDexter didn't seem to like that position as much - it was way too bottom heavy and somewhat lacking in presence.
To see how it sounded through an amp, I plugged the ToneDexter into the rig that I've been mostly using for upright these days: a Demeter Minnie 800D, which is Class D power amp (no tone controls, only output level), into a Bill Jenkins 112 cabinet. It sounded pretty good right away, though I had to back off the bass control on the ToneDexter to about 9:00 to get the amount of definition that sounded right, at least in the room I was in. The CH0 (focused mic) Character setting on the ToneDexter sounded the best to me. Comparing the ToneDexter to the raw pickup signal was startling, mostly in how honky and artificial the pickup sounded in comparison.
Out of curiosity, the next day I did a training pass with my DPA 4099B mic, aiming dead center between the F holes about 2" above the bridge, which is the position that seems to work best on my bass. It sounded pretty good, maybe lacking in the mic-like natural stringiness of the CM 67 wave map, but definitely more focused. I'll have to wait to see what works better in a live context, and I'm sure I'll do a lot more tweaking in the meantime.