The post clarifies: It’s dial.
It clicks as you turn it left or right and it can also be pressed as button. Each click of turning it left or right or pressing it can all be bound any keyboard or mouse function.
Mime is set to scroll with page-up and page-down when turned
A large trackball like the Kensington Expert can both move quickly across multiple 4K monitors and precisely point to a specific location.
By holding down a button, the trackball can also double as a scrollwheel.
The ergonomics don’t matter to me a lot because I don’t use it a lot. But I love the fast and precise movement.
As the trackball gets smaller, you have to choose between fast OR precise. Some smaller trackballs deal with that by having a toggle button so you can switch between fast or precise movements on the fly.