There's a thread going on now on one of the gun forums regarding stiffeners....some swear by em and some feel they are not necessary.
A couple things I've noticed about them.....a belt will soon form that s curve in them to conform to your body shape....a stiffener will fight that, and may prevent it all together....that will mean an uncomfortable belt.
Someone stopped by with a nylon belt that has a Kydex like plastic stiffener in it....the belt got folded in half, got sat on...now the Kydex has a fold in it that won't come out so the whole belt is folded at that spot.....can't heat the plastic cuzz you'll melt the nylon before you can get it hot enough.
The question I always have is, just how stiff does a belt have to be to do it's job?......I maintain two layers of leather equaling 1/4" (or even one layer for that matter) thickness, glued and stitched is plenty good.
But I guess if you believe stiffer is better....rock on.