It is basically the same mouse with two main differences:
(1) It is corded, not wireless.
(2) It is missing the thumb scroll wheel
Why am I switching? For some reason, ever since I purchased the really nice Logitech diNovo Keyboard it has been conflicting with the USB wireless connection of the mouse. So the MX mouse was skipping 5 to 10 pixels. As I tried to click on something, the mouse would jump and I would end up somewhere else. As you can imagine, it was very annoying and frustrating. I tried moving USB devices around – but it never worked.
So I moved to a corded mouse and so far, it seems to be working fine. I don’t miss the thumb scroll, simply because I never used it.
I have been a long time user of Logitech mice. In fact, when I replaced my Appel Mighty Mouse with the Logitech VX, before the Mighty Mouse I had a cheap corded Logitech mouse for years. Now, it seems I go through a new mouse every 6 to 12 months.