It's not so much an analog/digital thing - really they just work in different ways. The Subterranea is more of a waveshaper - it takes your signal, turns it into a square wave, and uses that square wave to switch a filter at audio rate to generate the "sawtooth" wave. I'm simplifying of course but that's the idea.
The Dubterranea on the other hand really is tracking the frequency and using that to control actual oscillators. In theory this could be done with all analog tech but I promise it would glitch even more and you'd have to keep retuning it as it warmed up throughout a set.
The downside with the Subterranea's approach is that it isn't a very accurate sawtooth, and how saw-like it is varies depending on the note you're playing. So in terms of the harmonics generated it's never going to sound quite like a real sawtooth. The Dubterranea does, but, the downside of its approach is that it's more prone to pitch-tracking errors if you don't play really carefully.
People didn't really seem to like the Dubterranea as much as I would've hoped, which is why I've never made more. There were other pitch-tracking pedals in the pipeline too at the time, which I decided to shelve given how that went. It's just a much harder problem to solve than people might appreciate - not just making it track well for my instrument and my playing style, but every instrument and every playing style.
Edit: unrelated but I just noticed I've officially been on Talkbass for 20 years.
Congrats on your 20 years Talkbass Anniversary hahaha!
As far as pitch tracking goes, are you aware of this company that makes audio controlled oscillator chips: ACO100 - Second Sound They seem pretty keen on providing pitch tracking solutions to other manufacturers, and theirs seems pretty solid with respect to tracking. I'd be really interested to see a pedal builder take that tech and make something like the DubT with a huge range of oscillator choice. Second Sound offers a pitch to CV / Midi pedal, but I think a lot of people would prefer something in the DubT format that is just a box with really great sounding and tracking oscillators without any extra bells and whistles (which I thin is the appeal of the DubT).
I struggled with the tracking of the DubT, but I LOVED the waveforms and choices it offered. For a while I ended up sending a pure sine wave from my Source Audio C4 into the DubT, which took advantage of the excellent tracking of the C4, and gave me all the sweet waveshapes from the DubT.
I found that the DubT actually tracked lows as good and often better than any other octave pedal I have tried, I found where it really struggled was with tracking higher notes. Not meaning any of this as a slag, just figured I would share my feedback since the topic came up.