I love my Marble Mouse (red ball) and have used it for many, many years, at work.
I don't know if the balls are interchangeable. The Trackball I got about a month ago is for home use.
The change of position for the ball makes a huge difference---the Trackball is a completely different mouse. I suspect that for all who are used to the Marble Mouse, this Trackball will be disappointing. I still use the Trackball, because I need a wireless mouse at home. But I don't at all have anywhere near the maneuverability that I have with the Marble Mouse. Which means the Trackball gives me none of the pleasure that I get from the Marble Mouse.