Well, it markets itself as ergonomic and all the reviews I've seen rave about how it "fits right in the hand". Well, no, it's not ergonomic at all and it doesn't fit in the hand.
For example, there is no comfortable place for the ring finger. It lays on the edge right of the right button. That edge is really not comfortable or ergonomic. The finger ends up laying on the right button alongside the middle finger, making right clicks inefficient.
And then there's the thumb buttons. In order to use them, you need to pulls back your hand so the thumb lines up with the buttons. It makes them unusable.
The scroll wheel does not stand high enough. Since the top of the mouse if angled, it is impossible to push the wheel to the right using your index finger. There simply isn't enough to push against.
I keep changing the position of my hand on the mouse simply because there is no natural position. That thing was designed for looks, not to fit in a hand.