I love the 9mm f/8 fisheye body cap lens and if you just want one unique photo and you can use a slow shutter, that’s plenty, but if you want to control focus, use a larger aperture, have a sharper image AND have the option to use fisheye compensation, you’ll want this lens. I find I often prefer it to the 7-14mm because it has a larger aperture and is really two lenses in one, both a fisheye and a regular wide (though fixed focal length) if you use the built in fisheye compensation.