My colleaugue uses one of these. You have to make a 'click' on the backswing then another 'click' on the downswing. But in order to make the backswing 'click' you have to either set the wrists early in your backswing or whip it away so fast you take the club by surprise!!

Not good for tempo....in fact not good for anything! e.g. the grip is such, that you can only grip it one way!