Originally Posted by Captain Evil
I've used something similar - a mesh sheet produced by a company in the UK which you soften in boiling water. That means you can usually use it on a yard (there's generally a kettle).
After a couple of test runs I've used it precisely twice, both times on really awkward horses.
The problem is that while it's useful if you need to go away from a horse, either to make a saddle or alter a panel, IMO it's still too flexible to guarantee a perfectly accurate fit based on its shape alone.
If you're a long way from a saddle fitter I can see it might be a better bet than a paper template for checking whether a particular saddle fits reasonably well. But it's a long way from perfect, unfortunately. Plus you have to have an oven close enough to the horse so the sheet doesn't go hard before you get there ;)