Automotive urethane such as Delstar is a catalized paint usually used on high performance models that have either fg covered balsa surfaces and or fg fuses such as many of the pattern and jet models. It's the most "bullet proof" of finishes out there and it produces a dazzling finish. Drawbacks are it is very expensive and potentially dangerous to inhale.
I would use it on model types as listed above but for scale types I would use two part epoxy or latex.