The biggest problem for me with the mouse was that the cursor tracking speed was so slow that it took a lot of effort to use it. This didn't change when I altered the computer's tracking speed settings, made sure the mouse was fully charged, used it close to the receiver, used it on a mousepad or not, or tried it while it was plugged in. This could be because the laser was positioned to the back right of the mouse rather than in the center.
If that hadn't been an issue, I would have kept the mouse but rated it three stars because of the design. Although it markets itself as ergonomic, it's much flatter than a normal mouse - which means I ended up having to use my fingers a lot more than my wrist in order to click, to move the mouse, etc. I have tendonitis that doesn't bug me much these days but was starting to bother me after using this mouse for just a few minutes - so if you have similar issues, this mouse may not work well for you either.
A less important complaint I have is that the instruction manual was obviously made for a wide variety of mouses rather than this one specifically. It referred to functions for buttons this mouse didn't have, LED features that didn't come with the mouse, etc. It made it hard to decipher how to use it when I couldn't tell if I was missing something because it wasn't on the mouse or because I just needed to look harder.
It was true to design and very aesthetically pleasing, but unfortunately unusable for me.