The Expert Mouse costs a lot, lot more than a simple trackball. And my subjective feeling is that it's actually less ergonomic than the cheaper Logitech I've got.
https://www.logitech.com/en-us/products/mice/mx-ergo-wireles...
There’s also the slightly smaller Deft Pro (https://switchandclick.com/elecom-deft-pro-review/) which I also own and use for travel — it has a superior scroll wheel and therefore may be a superior choice for you.
For me the Huge has a perfect form factor that outweighs all else.
On mac I use steermouse to map the buttons.
I promise to stop being a trackball pusher now.