It's a very comfortable mouse that is properly weighted (I'm not a fan of cheap, extremely light mice). I like how very customizable it is using the app you can download for free from the Logitech website. I also like how it is able to connect to the device via either USB dongle or Bluetooth. I recently purchased a new internal Wifi card for my laptop that includes Bluetooth. As a result, I can connect to my laptop with Bluetooth and not need to use up a USB port for the dongle. There is a button on the bottom that allows you to connect and easily switch between up to 3 devices. As it is Bluetooth I also have it connected to my large tablet.
The negative: 1. I wish there was a place to store the USB dongle in the mouse like Logitech does for their much cheaper mice. 2. The "Forward/Back" buttons are a little too small and too close together (Logitech seems to have corrected that with the newer MX models). 3. Occasionally, the Bluetooth connection between the mouse and laptop lags or drops for a second. Not a big deal for home use but if I were using the mouse for work I would definitely connect it using the USB dongle.