The shape of the mouse is comfortable
How is the shape?
I have had it.  This mouse is terrible.  I've got a cheap bundled no-name mouse on my laptop, and I'm stealing it and throwing this one away.  Even that mouse is better than this one.The biggest problem with this mouse is the tendency to double click when a button has been clicked once.  It started two months after I got the mouse.  At first it was now and then, making me think I'd clicked twice.  Six months later, it's a constant thing, probably about 80% of the time.The tracking is also not great.  With a mouse pad it's bearable, without one it's impossible.  Either way, sometimes small movements just don't happen at all.  I'm never really sure where the pointer will be when I move the mouse.The three year battery life was good for about 6 months.  To me that's not a big deal.  I've usually got batteries on hand because we go through them quickly in remotes, so if that was the only problem with this mouse it would hardly be worth mentioning.The shape of the mouse is comfortable, and the scroll wheel is fantastic.  But the mouse really does have to work properly before those things become important.For the primary computers I've owned nothing but Logitech mice and mostly Logitech keyboards since the day I gave up my IBM tactile click keyboard.  This mouse has been so frustrating that it has convinced me to give up on Logitech for good. 