OCIA.net has posted a review of the Razer Diamondback Gaming Mouse.

Some of the coolest features on this mouse are found in this control panel. Here we are looking at the overall sensitivity and the double click speed. Above that is the "on-the-fly" on/off switch. If you click this to "off", then button 4 will activate/deactivate that feature. If "on" is selected, button 4 will not function. What on the fly does is enable you to change the speed and sensitivity of the mouse during gameplay.