This is the best-selling hopper in the US for several reasons. First and foremost is the profile, which is spot on. The other key elements are limber rubber legs with angled joints, its specific density and how it sits deep in the film, two toned body and color selections, high-vis locator patch and its unusual ability to catch micro currents and move about unpredictably on the surface.
While these flies fish well on a standard dead drift, many anglers like to chug them a few times after landing or chug them continuously. Try it.