I agree with everything that Baddwin said.
I have both an N52 and a Saitek Cyborg. The main functional difference is dpad on the nostromo vs mini joystick on the cyborg. I kinda like the mini joystick better but the belkin product is a more solid build. But trivial differences.
Reasons I bought the thing:
1. Like baddwin says the control thing is the best ... In a perfect world people would have three hands so that one could steer the toon, one could position the mouse, and one could mash command buttons. However, apparently God's plan has us optimized for something besides MMOs I guess. But overall ... Being able to steer with a thumb on my left hand and then having the other four fingers for command keys while the right hand drives the mouse is really nice.
2. I often play off a laptop and it is vastly more ergonomically correct and comfortable to not have my left hand propped up on the laptop for extended period, daring carpal tunnel syndrome to descend on me.
3. Being able to dedicate the main keys under my left hand fingers to something besides WASD steering is nice.
4. Both of these products allow key profiles to be setup the are easily swappable ... With a physical switch on the device. For hybrid toons this is nice. Back when I was ambitious I had a cat map, bear map, etc.
Only downside is that is does take some getting used to and makes it harder to switch between using them and using a standard keyboard and mouse setup. Also the key mapping software is not exactly world class and kinda awkward. But overall I think they are great wow tools.