I think its a bad idea to try and replace the keyboard. I have played FPS games for long periods of time, and I don't agree that it feels cramped. If anything it feels very spacious, I have buttons very advantageously placed all around my hand, also I have a whole keyboard full of buttons which I can use for extra hotkeys in games.
This pad basically is giving you the left side of the keyboard chopped out, you lose a lot of extra buttons, and the buttons aren't all that greatly designed.
Personally I see PC gaming as using keyboard and mouse, not some customised controller with limited buttons for programmable game use.
But saying all this, I have large hands, maybe some people can't reach buttons further to the right of WASD.