I would like to mention 1 thing, shrinking disc is great, but only for certain applications,
One example of My experience has been with one particular door skin and bonnet, where the use of a shrinking disc worked fantastic, had the panel dead straight, but put it in the sun the skin and bonnet looked like the waves on a beach,
when cooled down they returned to normal.
The only way to rectify was heat shrinking with oxy, and start from scratch.
So both have there place and you have to study which one is going to work.