It’s ok on small dents, but I wouldn’t employ it if the damage were substantial. If it was badly damaged, as you say, it is probably beyond repair by PDR. Get a second opinion, and remember if the insurer decides to use PDR and the result doesn’t satisfy you, you don’t have to accept the car when it’s completed. If you are unhappy walk away and leave the car with the repairer and the insurer until it is fixed to your satisfaction.