I dont own one, but curate https://reddit.com/r/ergomobilecomputers where you may want to search for other tablet/iPad setups.
Theres been a couple Twiddler setups shared on there too.
I was experimenting with a Twiddler 3 for keyboard shortcuts on a Surface running Illustrator for a while. Started getting decent speed with my custom layout designed around my most used shortcuts. Ultimately I went back to a Mac laptop plus a drawing tablet, but this was because of issues with the Surface consistently dropping the first half a second of most of my stylus strokes, not because of the Twiddler.
Can you vouch for whether it's any good for the use case I had in mind (Apple Pencil + [thing] + iPad)? It looks neat in any case, thanks for the tip.