Pros: Tons of customization, very ergonomic
Cons: Yet another scroll wheel, plastic dome keys, no LED customization, learning curve
There is a learning curve to this product, the severity of which depends highly on how many keys you have mapped and how many macros/shortcuts/keymaps you have in use. By default, the device is configured to emulate the area of the keyboard that most people use with their left hand while gaming, the WSAD cluster, and so the learning curve mostly comes from having to space out your fingers in a slightly different way to reach the space bar, and from the d-pad which now sits right near your thumb. Once you start to customize the device to your liking though, it an take some time to get used to where everything is, but once you do, you'll never want to game without it again.
I only have two major complaints for this device. My first would be the scroll wheel. There's no reason for it to be there, and most of the time I disable the up/down scroll and just use it as a single button press anyway. I feel that the scroll wheel is extraneous and would have been better as another button. The second is that the keys are plastic domes instead of mechanical keys. I feel that a mechanical switch would serve much better as most gamers mash on their keys very heavily. My other complaints are very minor (no way to change the LED colours other than hardware mod, finish is shiny and not matte).
Overall, I find this device to be a solid buy, especially for gamers who need a lot of action bars or shortcut keys right at their fingertips.