Well, seems like I've answered my own question. The Gear4music site allows you to filter pedals by analog or digital. The Eden WDTI Preamp only appears among the analog results.
https://www.gear4music.com/bass-guitars/effects-pedals/preamp
Interestingly, my Beringer BOD400 overdrive pedal, which I always assumed was digital, is also listed among analog results in its category. https://www.gear4music.com/bass-guitars/effects-pedals/overdrive
I don't understand, how does it minic valves so well with just a cheap solid state circuit?