I bought Q-tron nano because my EHX Bassballs are quite limited in tone capabilities.
Although I love few sounds that Bassballs gives me and especially the design of the pedal, I've always been looking for a Flea sound from the BSSM album.
Speaking from a bass player's point of view, BP and HP Modes are practically unusable, so the LP Mode remains, but it's enough. Quite enough bass goes through the pedal and there are no losses.
If we leave aside the VOL control which only controls the volume of the pedal, there are two controls left, Q and Drive which shape the tone, and that's really what makes this pedal interesting.
After a direct comparison with Bassballs and by watching videos of envelope filters from other manufacturers, I must say that I am quite satisfied and that the Q-tron nano will find its own small space on my pedalboard.
To summarize, considering that the old original Q-tron that Flea used is quite expensive and takes up a lot of space on the pedalboard by today's standards, my choice of Q-tron nano was jus what I wanted - no regrets.
Update January 02, 2023.
Replaced it with MXR Bass Envelope filter. Different category in all ways, and also different price range, but I think my search for envelope filters ends now.