Brand new trackballs can sometimes have some stick-slip. But they "wear in before they wear out" with use. Popping the ball out and cleaning it with warm soapy water and a rinse helps a lot. And whenever the ball feels sticky a wash is in order.

My current Logi tech ball mouse had a tiny defect in the ball that a minute's worth of 1000 grit wet/dry sandpaper fixed. It's now rolls like it's running on air bearings.