Dumb question but is this the type where you use your thumb or your fingerd to control? I see conflicting comments below. I have a few trackballs but prefer by far the centralised kind rather than the thumb kind.

You control the trackball with the fingers of your right hand, and there's a scroll wheel and right and left buttons under your right thumb.

The Ploopy Adept is their central ball model. This is a top ball.