Undercarriage Paint – Herculiner

Happy Friday All, I was looking at a ’74 dart this week and saw an interesting application of Herculiner. The owner had coated the undercarriage and rear wheel wells with it. I know POR15 makes a rubberized product for a similar application, however I’m not sure of the differences between the two. Is there any concern with this approach? I didn’t ask if he treated with a rust preventer prior to painting it. Appreciate any thoughts.