All well and good...
But for my money I'd buy the Logitech MX310 any day of the week for the rest of my life.
Cheap, good weight, not too many buttons, lefty and righty friendly.
Used to be able to find the OEM versions for about £12 a couple of years ago... Wish I still could.
Not that I need to buy any more... I've got two, and they'll probably last longer than I will (one even did 30mph on it's back out of the door of my car when it fell out with the lead trapped, got some great battle scars, but still works fine!). But I'm always bumping into people who still have ball mice full of fluff! Dell seem to keep shipping the damn things!