What I wish I'd known before getting into split keyboards: definitely results in better keyboard ergonomics, but worse pointing device ergonomics.

If your keyboard halves are perfectly aligned with your arms, your pointing device won't be. If you move it in the middle of the halves or to the side, it hurts.

Gotta move one half in a bit to make room for it, which makes you want to ease the other half in too. So both halves end up very close to each other… like in a normal keyboard.