I have moved from the excellent Mionix Neos 7000 mouse, to the Logitech MX Ergo Trackball... and I am quite pleased. Yes, shoulder pain was a major concern, I will still keep the mouse for games and such. but for CAD and 3D work the Trackball has proven to be much less painfull and more effective, even if YES, there is major getting used to it. Mostly, precision issues, as I am used to high DPI mouses and gentle movements making great spans on the screen, simply to preserve my muscles and do as much as possible moving as little as possible, the trackball is amazing at that, BUT precision with a thumb after years with precision at the wrist get some time to get used to. Also, some movements which were second nature on the mouse have to be re-adjusted.
Now, that said, I am a Blender and Rhino user as well. And those software have one very minor detail which makes the trackball become one major advantage over archicad. If I want to move to great extents, in Rhino and Blender, I can just move over the screen side, and the mouse will keep moving to the infinite. That is both true for mouse or trackpad or trackball. BUT, on the trackball you never run out of "table surface" to scroll over, being able to really feel the freedom that feature gives. It in a short, if you know the workspace, and the design you're working on, saves a few "Zoom Out, Zoom In" to click on a small detail and click on another small detail say, 7000mm ( or two screens ) away. I could click on the small detail and move sideways just rolling the ball until I find the detail to connect to. On Archicad, I am having to zoom out and zoom in again, because when I instinctively tried to do this, the cursor would hit the screen end, and that would be that. Not sure if there is some function I could enable to that that happen, but it is so far the only point where a mouse ( where zoom in and out become far more common on the workflow as the table is limited and I cannot simply roll the cursor over an infinite surface ) versus the trackball ( where I could just roll as needed in theory ). It is a little bothersome detail I am facing now while detailing cabinetry in a kitchen, so, I felt it was work to mention.
Overall I think both have advantages and disadvantages, since I am a notebook user, being able to work on a sofa, with the trackball on my leg while the notebook is on a small table by my side, and not have to worry about the mouse pad and such... is also a bonus
But it is big and heavy, not sure how it would cope on traveling yet. So, much much better than bad, so it's good. Advantages over mouse, but the biggest one is injury prevention for those who are already feeling their wrists and shoulders complain. And in a few software, this gesture-saving feature of rolling beyond the screen to reach elements without having to resort to the scroll wheel.