I think this is reversed. Assuming that the position of the pad relative to the pivot is the same, longer extension of the arm yields *greater* mechanical advantage for the pad's contact on the rim. However, this requires a corresponding increase in cable travel which may not be available depending on the brake levers.
The reach extenders in Ron's post (#12) effectively shorten the arm from the pad to the cable attachment, which *reduces* the mechanical advantage over the original pad position.
As you say, it's whether the brake works well enough that is the important thing.