stainless steel vs aluminized steel, mandrel bent vs regular bent

Dougs look good. They've also been around a lot longer than TTI. Since I have had both on the Dart, I wonder if TTI got most of their design from Dougs, and improved it with the step version. My TTIs have just the nickel coating and do not have any rust. They have to be on 5-6 years now. Just to reiterate, I wouldn't go near an exhaust shop that does not mandrel bend. Its like going to a tire store that doesn't have a balancer....