yeah I have bought that particular finish by the semi truck load in 5 gallon cans.
lay one of those doors out in the weather and tell me how long it lasts
We used to buy a product called fabulon which was far better than helmsman
but its not good enough for weather either.
and thers a line of professional grade called Dura-Seal its the parent company of Minwax
and again I have literally tried them all ( all the good ones, I didn't try "freds" polyurethane)
We wanted a poly that could be used on semi covered porches and decks, never found one
We had to use a silicone based protectant that soaked in rather than producing a film.
I'm just trying to save some folks money and trouble,
Moisture cured urethane might last a little longer but nothing is going to last like we would want it to.
except maybe a properly bonded rubberized coating.
My .02 cents