I got this a few weeks ago interested in the unique features it offered. What a waste of money. I hated it almost immediately.
Ergonomnics - The shape of it is like a small box. About as non-ergonomic as you can get. Convinced that it was 'cool' product that I just had to ease myself into, I forced myself to use it and got used to the weird shape after a few days. But my hand began to hurt pretty easily from being in such an akward grip all the time.
Scroll Pad - The whole 'scroll pad' thing.... Not a good idea... It's interesting and new and unique, but if Logitech replaces all their scroll wheels with these things I'd have to start buying other mice. I had an incredibly difficult time with it in some cases. It is good for scrolling up or down on long documents or webpages. But it is HORRIBLE for when you need precision scrolling. Like if you know you need to move the scroll wheel up exactly 3 "clicks", it is virtuall impossible, unless you get lucky.
EXAMPLE - You are playing some FPS game and you use the scroll wheel/pad to change weapons. You are using the pistol and you have to scroll up 2 "clicks" to get to the shotgun. With this mouse, GOOD LUCK!. You will either overshoot or undershoot almost everytime and end up with the wrong weapon in your hand. Impossible.
COLLAPSING - A cool unique feature is that the wireless receiver can fit into the bottom of the mouse and it collapses upon itself for easy storage/travel. A cool idea that works very well.
NO MIDDLE MOUSE BUTTON - I use the middle mouse button all the time in my field of work and can't use this mouse without it. Logitech decided it was a good idea to get rid of it for some reason. Probably cause making a clickable scroll pad was too complicated. Anyways, BAD MOVE.
Overall I give this mouse a 3/10 (10 being the best). I like the collapsing feature, but there are too many other problems with it. Too uncomfortable, scroll wheel too difficult to work with, and no middle mouse button.
In my opinion, if you want a really great and comfortable mouse, buy the Logitech MediaPlay mouse. I own 3 of these things for my computers. It's wireless. Perfect for either left or right handed folks. Very ergonomic. And the wireless is very responsive. IMHO this is the best mouse Logitech has released since the original 3-button MouseMan many years ago...