Having an Alpha and a pico (just a player), I'd be interested in what you want to accomplish. Is it a price of entry thing?
Anyway, here are some reactions:
I think that there is a difference between a smaller Tau and a larger Pico because their application differs.
There is likely no great advantage (price or playability) to a smaller Tau.
A slightly less cramped Pico would be nice but should maintain its usage (hold-ability similar to a wind controller).
Honestly, a pico with an extra 8 playing keys would bring it up to the size of other wind controllers and go a long way to lessening the use of octave switches. I'd also move the octave switches to the back; perhaps either side of the thumb hook. I would not add percussion keys.
While we are making a wish list, it would be nice to have some solutions that 'port' ornamentations from monophonic instruments (cuts, strikes, bending into a note, etc) which might be possible withe a second thumb sensor on the back implemented with an agent that applied to (only) the next note played as an articulation switch for example.
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