Happy Charybdis user here. If you ask, I'm sure Quentin would be willing to build a Charybdis with a trackball on both sides - he was very accommodating of a change I requested (I wanted ball transfer units). He already supports having the trackball on either side.

(I'm not OP - I'm on the Charybdis.)

I prefer a trackball because I can momentum-flick my cursor from one side of my 4k screen (at 100% zoom) to another side monitor pretty easily... as long as I keep the ball bearings clean. I've been thinking about using a metal trackball for more momentum, but haven't gotten around to it yet.

I have a "sniper" key I use to decrease sensitivity for more precision cursoring... but rarely use it (maybe once a month?). I do not have thumb fatigue.

I’m loving it! It was quite the jump from a standard layout to split + ortholinear + column stagger but within a week I was comfortable using it in the office.

No strain from using the ball, it is (or can be) quite sensitive so you only need very slight movements and as another poster mentioned there are a variety of ways to adjust the sensitivity of the ball on the fly via layers for speed vs precision.

It’s entirely programmable, and easy to do so, so if something isn’t working or doesn’t feel right it’s you can adjust every key and ball function to behave as you’d like.

Was also very fun to build - but you can buy them prebuilt too