Are you sure that the door you need? Looking at the specs, it has no weatherstripping...
Does your shelter have another, inner, door? Because the one in the link isn't a storm shelter door...it's just a basement hatch.
This is what I thought after looking at those doors. This would not be a FEMA rated door and I wouldn't trust it to keep my family safe. A basement door isn't the same thing as a storm cellar door.
Like everyone else said, I think you would be in much better shape refurbishing the existing door if it looks structurally sound.