Actually it was this one.
http://www.logitech.com/index.cfm/products/details/US/EN,CRID=2150,CONTENTID=5002
I was debating on buying the first one you linked, but when with the thumb version.
You can't go wrong with the Logitech model there if you favor a thumb ball rather then the index finger type. I actually gave away the MS version of that called the Trackball Optical. You can see what that looks like at http://www.microsoft.com/japan/hardware/mouse/track_optical.asp
When I lliterally wore out the first T.Explorer that was the only model seen in a local office supply store and Circuit City alike. The T.Explorer is only found on amazon.com these days.

