they had one of the best sensors ever, but it's only 400dpi.
I hated the 3.0 myself though cause of it's piss poor button quality, whenever I used it it would just randomly fire shots
Wheel mouse optical>3.0 imo
I liked the intelli 4.0, but that one had piss poor quality as well. the mouse2 button broke on every single one I had(and I had like 4 of them)
had the mx500 before the 4.0 and went back to 518 when they came out.
now I'm running a g400s and will mostly likely never change.
this is the mouse I wish logitech would bring back with an updated sensor though.

my first optical mouse ever, loved it to bits. But the sensor is of such poor quality that it will randomly just go bonkers.
Maybe I'll try adding some new hardware to it at some point.