I've always preferred a trackball to a mouse, (I always know where the trackball is, my mouse, not so much) but the utility of the scroll wheel had me using a mouse. The scroll ring makes this trackball complete. I was worried that I would find the scroll motion awkward, but I instantly became used to using the ring to scroll.
I used to use a Kensington Turbo Trackball at the office and always liked it a lot. Picked this up today at my local Apple Store (based on price and basic functions) and got more than I thought. It's got a very small footprint (unlike the old ones) and the ergonomic extension is actually very comfortable. The overall functions and actions on this trackball are excellent. Glad I made this choice!