Does anybody have a favorite mini controller that you love? I suspect 25 keys are not enough. Getting to 32 or 37 can be a good trade-off. Higher key counts for me are acceptable only in a folding configuration, because my transportation means are very limited for this use case. As such, mini keys are preferable, as long as their "feeling" is decent and not too awkward.

Must have:

small footprint (20" is too much, but can be acceptable is everything else is exceptional, 18" is borderline, 16" is good, less would be fantastic)
USB-MIDI (to connect to phone for getting decent audio, or alternative great sounds of its own, which I doubt any non-MIDI keyboard would have).
decent velocity sensitivity
a way to accept sustain (pedal preferred, switch/button on the thing acceptable)

Must not have:

too many non pianistic buttons, pads, pots and the like, because they would take space and are prone to get tangled with other crap which I toss in the same backpack

Bonus points:

aftertouch, especially if polyphonic
clean look
soft case included
speakers even if small and low quality
work on USB power from the USB-MIDI connection or its own batteries, rather than with an AC-based power suppy

Random ones which could fit the bill

https://www.amazon.com/M-Audio-Keystation-Ultra-Portable-Keyboard-Controller/dp/B07GBNNF23/

Alternatively this one has the same number of keys, but they are in a different configuration and it is slightly larger
https://www.amazon.com/midiplus-32-Key-Midi-Controller-AKM320/dp/B00VHKMK64/

A 3-octave one
https://www.amazon.com/GarageKey-Mini-USB-MIDI-Keyboard/dp/B005WKK3XM/

Foldable ones
https://www.amazon.com/Carry-On-49-Key-Portable-Keyboard-FOLDPIANO49/dp/B08WY6J7XQ/
4 octaves, when folded smaller than most of the above!

https://www.amazon.com/Blackstar-88-Key-Portable-Keyboard-FOLDPIANO88/dp/B08M1L9KNJ/
full piano compass, smaller in length than anything else, at the expense of being thicker (I know on this one option there was an old PW discussion, which I will dig out later today)