Excerpt: I've become accustomed to using a contoured mouse, so using a "standard" mouse even for a little while seems wildly uncomfortable.
I recently built a new PC and decided to try the Logitech M500. I'm very happy with it after 3 weeks.
It feels fantastic in my hand.
Pros: I've had two of these mice. The first one lasted a few years with heavy use. I bought another because I liked the first so much. The second one has lasted longer but I use it less often. I would buy another if this one failed.