Lesco has sold RUST ERASE for year. It is oxalic acid. Of course the great thing about oxalic acid is the minimal impact on soil and plants
Paver's and other surfaces where I don't want to take a chance, I use Household Vinegar. From an experience on Black Top road I found oxalic acid clean TOO good and leaves a Clean spot that takes years to blend in. Yes it takes Multiply applications of vinegar which is a PITA, but having to replace a Paver Brick Driveway isn't cheap.
Muriatic acid not only tears up surfaces, But it can sterile the Ground and kill plants and trees.
it is one thing to do a off label applications. It is total stupidity to post it on the world wide web and expect people to approve.
You can lead a Donkey to water but you can't make the Jackass Drink