If you don't have fat fingers, get the
Ideazon Fang. I've been using one for about 2 years and I've gotten to the point where I can't play competitively without it. Between the Fang and my mouse, I don't even touch my keyboard, aside from switching the LCD to different screens depending on what I'm doing.
I'm a huge fan of the Logitech G line of products. My G15 will be replaced with the G510 next month, my Performance Mouse MX will be replaced with the G700 next month, and my wife is getting me the G930 headset for Christmas.
With that said, the G13 went back to the store within 24 hours. The slope of the G13 is awkward. If you rest your fingers on the top row, the bottom row is almost impossible to reach, since the rows slope down. If you rest your fingers on the middle row so you can reach the top and bottom rows, the thumbstick becomes awkward to use. You end up resting the side of your thumb on it instead of laying your thumb flat. Also, being so used to the fang, the G13 could really use another 4 or 5 buttons.