I'm loving my twiddler, currently learning to type with it, but the one thing it lacks is a good mouse.
The joystick is passable, but i think a trackball - a very small one at that - would much better, and easier to use.
I'm planning on possibly diy-ing something like the "Trackball Breakout by Pimoroni" or harvesting a presentation mouse trackball onto another twiddler at some point, to see if it would work.
I just thought id suggest this, as many small thumb trackballs exist, and I think it would really help it do everything, cause as a mouse, it is generally just cumbersome. Or even a more joystick like trackball, or something like the 3ds's joystick. I think thats really a great place to improve.