I take the 180 degree opposite approach.
I do not see the point of spending $$$$ trying to armor-plate something that is used in extreme conditions anyway.
My choice is plain old water-based exterior latex paint.
It is extremely tough when cured and is easily touched up.
I would rather spend $15 for a quart of paint that lasts forever and uses water for clean-up than all this fancy-dancy stuff.
First time preparations is to power wash it. Wire brush any loose rust and hit any rust spots with Rustoleum rusty metal primer.
Then topcoat with the latex. I use either a foam roller (available in various widths) or a chip brush. Foam rollers and chip brushes clean up easy.
That's it. Dries to the touch right away but takes a few days to cure completely. You can hit it with a hammer after it's cured. And, as I said, touch-ups are easy.
EDIT: Depending on how you apply it, you can achieve a textured finish. Foam rollers tend to produce a slightly textured finish. Brushing flows out smooth. You can brush first and then roll with a dry foam roller for a very smooth finish. Foam roller alone for more texture.