Looks really good. I thought of this too while doing the exhaust system. Here was a nice shiny truck with an exhaust that looked like it was buried on the Titanic, which I replaced. I painted that raw un-coated drive shaft, differential, and frame in spots. I used that rust prep without paint, your looks more shiny. Atleast if I don't get around to painting with POR 15 etc. it is black (the color the rust prep leaves it).
I also did the front suspension knuckles that are raw cast iron. Any of these make the truck look so much better IMHO.
I keep forgetting about this product you showed in your photos and nice to know Amazon has it too.
2004 F150 F x 4
2013 H-D V-Rod Muscle
2010 Cadillac CTS Sportwagon
2013 Chevy Volt