The Sto-Fen Omni-Bounce for 580EX/580EX II creates a bare light effect from an accessory Flash
such as the Canon 580EX Speedlite Flash.
Lighting coming directly from a small flash head is typically
harsh looking on your subject because of the sharp, strong shadows.
If you are in a small room with a white wall and/or ceiling or have another white reflective surface,
you might have an application for the Sto-Fen Omni-Bounce for 580EX/580EX II.
The Sto-Fen Omni-Bounce for 580EX/580EX II is very simple design - a single piece of molded, translucent, slightly flexible plastic. It mounts on the head of a flash using a friction fit (which I have found to be adequate). There is no Velcro to mess with and installation/removal is very easy. It would be hard to damage an Omnibounce unintentionally. The 580EX version has a slight domed top to accommodate the pull-out diffuser/catchlight reflector.
The bare bulb effect of the Sto-Fen Omni-Bounce for 580EX/580EX II causes light to be scattered in almost all directions from the flash. Some light will directly hit your subject and some light will be directed at your subject from the reflective light sources nearby. Shadows are reduced and softened - and the resulting is generally better.
The Sto-Fen Omni-Bounce for 580EX/580EX II will do very little without a reflective surface. Many people put the Omnibounce on their flash and leave it there. However, without the reflective surface, you get a very similar light source as you get with a bare flash head. One slight advantage of leaving the Omnibounce mounted is that the light source will be slightly farther from the camera if used in the recommended 45-60 degree flash bounce setting. You will not notice the difference if you are not close to the subject. The big disadvantage of using the diffuser without a reflective surface is that you cut the power of your flash significantly (by a factor of 2.5). Your flash will work harder and you will drain your batteries faster.
When looking at comparison pictures taken with and without the Sto-Fen Omni-Bounce for 580EX/580EX II, make sure you are comparing apples to apples. Make sure the exposures are identical on both, make sure the subjects are 100% identical.
The Omnibounce has Macro flash applications as well. Typically, an on-camera flash will not be able to aim down far enough to light a Macro subject right in front of a macro lens such as the Canon EF 100mm Macro USM Lens. The Sto-Fen Omni-Bounce for 580EX/580EX II redirects enough light down toward the front of the lens to light the close-up picture. Some of my insect and flower shots were taken with this lighting method.