> Am I correct in thinking that the main advantage of the horizontal
> 'power' handbrake is that it has internal gears to give some
> mechanical advantage, while with the staff your only recourse was a
> brake club?
Yes, Gerard, you are. Judging by the ads, and the articles in the trade
journals of the time, the main selling point was the mechanical
advantage. Many proprietary handbrake mechanisms were referred to as
power handbrakes for this reason.