I got interested in these split ergo keyboards when I saw the new Kinesis models [0] but unfortunately they don't ship to my location.
I came across the Charybdis [1] and I loved the idea but I'm not capable enough to assemble it myself and the guy making them has a many week lead time, so I'd love an equivalent.
Honestly though I consider mice and trackballs a crutch and really only for design work or gaming.
I ditched a mouse at my last office entirely favoring mouse emulation mode on the ergodox, a tiling window manager like i3, and the keyboard driven qutebrowser.
I had the CST between the halves for almost 8 years but recently went back to putting it on the right side.
My conclusion is that there are general principles of ergonomics but in the end you need to listen to your body and adjust if you feel pain.