* Positives:
This mouse helps prevent a pain in my wrist that I get when I use a standard mouse for an extended period of time. You grip this mouse at about a 45 degree angle, which is a much more normal angle for the wrist. It definitely helps me. This doesn't necessarily mean it will help you the same way, everyone's different, but it is certainly a much more natural angle for the wrist to be in for longer periods of time.
The mouse wheel of this mouse is the best I've ever used. It's effectively perfect for scrolling through web pages. Just the right speed and feel. There are no 'clicks' when you use it, but it still is precise enough to not need them, which surprised me, as my last mouse had the clicks and I was quite used to them. Scrolling is fantastic.
This mouse also has a sideways scrolling feature, if you need to scroll across wide spreadsheets or web pages. You can also reprogram this feature for other uses, if you don't need the horizontal scrolling. In fact, all the buttons are reprogrammable, not only globally, but per program.
* Neutrals:
The base of this mouse is notably narrower than the mouse itself, which while not a problem for me or my desk surface, might be for others. Something to consider.
The two thumb buttons on this mouse are way higher than any other mouse I've ever used or seen. You have to lift your thumb quite a bit to use them. I sometimes have to look at the mouse in order to find them.
Because the mouse takes 2 AA batteries, the mouse is quite heavy compared to a corded mouse. If your mouse surface is angled at all, this mouse may start to slide down it on its own.
Mouse click feel is average. It works. It's not great. Definitely not a gamer's mouse in terms of precision or feel. This may be a laser mouse, but it doesn't feel like it. I've tested it on various surfaces, from fabric to wood to glass to gaming mousepads, and the tracking is merely average - not better than my 4-year-old 'gaming' optical mouse. Nothing special here. In fact, probably slightly worse.
* Negatives:
The wireless receiver has almost no range. Like 2 feet max, with a direct line of sight. If you plan on putting the receiver where there might be stuff between it and the mouse - whether it be of wood, plastic, metal, or even a stack of paper - forget it, buy another mouse. The receiver practically has to be sitting on top of the mouse for it to work properly, and the receiver's USB cord is NOT long (maybe 4 ft) - so make sure after hooking up the receiver from your computer to your workdesk that it will still be within 2 feet direct-line-of-sight to the mouse.
A very odd aspect of this mouse is that it tracks slightly differently than any other mouse I've ever used. If you drag the mouse perfectly horizontally from left to right, the mouse will creep slightly lower as you move right. It's almost like the mouse needs a front-end alignment. So you will probably need to relearn how to drag this mouse in order to get the pointer to go where you want it to go. It's X / Y axis seem to be rotated about 15 degrees off from normal. Unfortunately, I've found no way to modify this in the software. Quite odd. Other people have mentioned it, and it is indeed true. It's unlikely this mouse will feel "familiar" to you as soon as you use it. The shape already takes some getting used to, but this additional tracking 'error' makes it quite a bizarre relearning experience.
* Final Verdict:
I'm keeping it because it helps with the wrist pain. I'm not loving it, though. If you really have serious wrist pain, this mouse might help you out. But that's about all it's going to do. Don't buy it for anything other than it's ergonomic features. If Logitech comes out with a mouse similar to this, I'll be buying that one quickly.