You can read more about it here.
http://www.npcompleteperformance.com/wotbox
Basically it enables you to keep your foot to the floor the whole time, when you press the clutch in it cuts the ignition for a few milliseconds (time is auto or adjustable) which then enables you to slide into the next gear like butter, assisted powershifting basically. (without the harsh effect of rpms being kept up while shifting)
It also comes with a two step feature, nitrous window switch, and the option of using it as a shift light.
pretty sweet device!