Check out this video of artist TerraTerrific using the miniature 8bitdo Zero game controller as a bluetooth hotkey gadget on the iPad, executing commands like “undo” and switching tools without having to interrupt the painting hand.
Unlike a standard bluetooth keyboard or full-size controller, the 8bitdo Zero fits easy in the palm. And unlike specialized art gadgets, it’s cheap.
I reviewed it a while back. It’s nice, but so small it’s difficult to play with, and a pain to pair. So this is a better use for it!