seems to me that they are relying on the aluminium plate to get higher pressure at the contact area where the toner covers the paper.
i've always used an electric iron, and i would get the copper hot enough to actually discolour (500F+?)
anyhow, seems to me most people have either tried to use special papers (such that most of the toner disconnects from the paper without effort)
i was actually getting half way descent results using standard copy paper, and a 100$ laser printer.
i would then wash the paper away in very hot water.
the problem i ran into was not enough toner coverage, such that the copper left behind was only 50% of the copper originally on the board.
this is however, a toner and laser printer specific issue.