Source: http://www.megalextoria.com/wordpress/index.php/2017/03/10/color-computer-magazine-november-1983/
While the joystik controllers that came with the Atari 5200 were pretty awful, this trackball controller was outstanding. This thing was huge, probably nearly half the size of the Atari 5200 itself which was a big system, and built like a tank. It was great for games like Centipede and other arcade games that were created with a trackball in mind.
I believe this add is from 1983 so this trackball would have been released in the spring/summer of 1983 which was about six months after the system was released.
At any rate, if you do decide to get an Atari 5200, get this trackball also and all the games that work well with a trackball (Centipede, Millipede, and Missile Command among others).