I have a coworker who uses one of these. They seem to like it, I tried it but it's not for me. I don't really have wrist pain issues, though I've started to wonder if the people who are helped by this kind of mouse are people who previously used the palm grip? it seems ever since they started trying to make mice ergonomic it really just promotes people resting on it when they shouldn't. I've always held the mouse with the claw grip and I've never had any problems. for reference: http://i42.tinypic.com/11il9jt.jpg
I rarely ever put my weight on my mouse with that grip although with the palm grip you almost have to. In fact, with the palm grip to move the mouse you basically have to move your wrist. Almost like as if you turned your head every time you wanted to look around, instead of just moving your eyes. I bet your neck would hurt soon enough.
Once you use the claw grip for long enough you can make many movements with your fingers only and with almost no wrist movement at all. However, this also means you generally want to use a smaller mouse, rather then the gigantic supposedly ergonomic ones. I used to use the plain old logitech optical mouse (then later an mx300). these mice all tend to be the smaller ambidextrous kind and are not "formed" to your hand in any way.
Same thing with keyboards, a lot of these ergonomic ones all have giant wrist rests and seem to promote resting your wrists on it even. They almost all say "don't rest your wrists while you type" in the manual too, which is pretty funny. As if that'll stop the inevitable. My favorite keyboards are old mechanical switch keyboards (buckling spring are 2nd fav...) but anything that isn't retardedly large and without a rest is fine. I use a pretty basic logitech keyboard at work and it's generally fine.
good posture doesn't hurt either. if you're sitting all hunched over...you know what to expect.