I suspect whoever is making these preformed stair nose planks has to have an efficient set up. You know they’re not sitting on the floor in their shed monkeying around with a router and a heat gun. If you had a shop and the right equipment it would be a piece of cake. Rather than using a heat gun you might have a 4’ long heat source or an oven? To heat the entire piece evenly. Then a modified sheet metal press break or something of the sorts would bend the entire thing as one uniform piece. For a bullnose you would want a mold or something to form the radius after making multiple kerf cuts on the back side.