http://www.logitech.com/en-ca/gaming...o-gaming-mouse

Has anyone used one of these before?
From the reviews I've seen, it looks to be well built.
Ergonomically, some prefer Razor Naga and some the G-600, more depending on the size of one's hands -- I've never tried a Razor Naga, but the G-600 feels good for me.
It feels close to (but slightly lighter) than my Logitech G5 mouse; moving it with thumb and little finger is a little different from thumb and ring finger, but muscle memory comes fairly quickly.

This has a left/right mouse button.
A scroll wheel, which counts as G3 (clicked), G4 (pushed left) and G5 (pushed right).
A G-Shift button (where the ring finger rests).
G7 and G8, below (closer to the palm) the scroll wheel.

And then 12 (G9 through G20) thumb buttons.
Three Rows of four buttons each.
A B C D
E F G H
I J K L
With ABEFIJ angled towards each other, forming a group of six.
And CDGHKL also angled towards each other, forming another group of six.

If you want to push and hold the G-Shift button, you can make each of the other G-Buttons do a different function.
Most of the reviews I've read/watched, suggest using that button for the Ventrilo/Teamspeak "Push to Talk" function.
It doesn't seem that comfortable, pushing G-Shift and a Thumb Button together.

I wouldn't really consider Left/Right clicks or the Scroll Wheel to be five G-Buttons, nor the G-Shift to be a sixth.
Still, that's 14 actual G-Keys, on the mouse.
Plus the regular Left/Right and Scroll Wheel.
And an optional "Push to Talk" on the mouse itself.

With the software, you can set three profiles for any given game.
And illuminate each with your choice of 16.7 million colors.
I'm planning on clearing the profile, and giving IS Boxer another 14 G-Keys to work with.

Leaning towards...
Thumb Buttons: Slot 1 through Slot 10, and Follow / Spread Out
G-Keys below scroll wheel: Key Map and Repeater Toggles.
G-Shift: Ventrilo's Push to Talk.