we can see how its assigned here: MPE layout
I’ve noticed a little trend in this area, where some developers/manufactures are just taking MPE as a ‘protocol’, rather than a description of per note expressivity, and in particular polyphonic expression.
basically this means it can means as little as using CC#74, Channel Aftertouch and pitchbend (or even a subset of these) on a note channel - rather than capabilities of a device.
so given the above mapping description my assumption is that this device, probably reads the motion/joystick at the time you press a note, and then creates a note channel with those settings… then if you play a new note (without releasing first note?) moves to the next channel.
this would give a ‘use’ for MPE.
(if it always just uses CC74/AT/PB on all channels theres not much point to using MPE - imho, global CC etc would do the same thing)
but yeah… it does highlight if you see a controller supporting MPE, do not assume polyphonic expression , go check the details.
I think it’s a shame that this confusion is going to arise, but I can’t say it’s ‘wrong’, if you need to use MPE to provide certain functionality to your controller (that can’t be done without) and it makes the user experience better… then for sure use MPE.
(in fairness, MPE was tried to be specified in such a way, that it allow for a wide variety of controllers with very different characteristics)