I bought MS's bluetooth 6000 series mouse a while back. Support was atrocious, the mandatory driver install frequently crashed my system, and tracking was delayed by half a second in many cases. This was when they introduced their "blue track" tech.
If MS has actually managed to improve more than the marketing of their mice, I'll eat that useless stainless steel piece of crap.
It’s also one of the first mice the company has introduced with a four-way scroll wheel which allows users to scroll horizontally by tilting the wheel left or right, and vertically by rolling the wheel up and down.