It can only shift as fast as your hand and gearbox allows. It's still all down to your hand etc.

It's just a mechancial setup that changes the fore/aft motion into the motions required to move the box into each gear, via various cams etc.

There was a nice video on youtube where a college student made his own for his Mini, cant seem to find it though. It had good drawings, computer images and ran through getting the parts all cut out etc. Cant seem to find it though