The only difference in the filter sections as far as I know is that the Enigma filters down to 40hz vs 80hz for the Riddle and the Riddle in turn filters up a bit higher for the guitar range. The Enigma can filter below the audible frequency of my basses (the bottom 1/5 or so of the Frequency/sweep knobs are just silence) so that extra sweep doesn’t actually serve much purpose. There are a few TBers that prefer the Riddle over the Enigma with bass for this reason. The Distortion sections are voiced different too, but I rarely use the Distortion on my Enigma so that part doesn’t matter to me much.
As I pointed out earlier, the Nano Qtron lacks the control over static (non-enveloped) filter sounds that you can be dialed in- the same limitation that pedals like the MXR and DOD have. So you will basically be stuck with whatever cutoff frequency is at the bottom of the sweep of that pedal when you turn the sensitivity control off, which may or may not work. You’d have to try one out to see if it works for you in this regard or maybe someone else can chime in who has tried it with the Drive turned all the way down.
The Enigma and Riddle both have Frequency controls that allow you to choose exactly where the static/fixed filter cutoff frequency is just like the Moog and Xerograph pedals do, so in that way they are superior for what you are looking for vs the Nano Qtron (they also have jacks for an expression pedal so you can manually sweep the filter, which is a popular modern electro dub trick, ala dubstep).