I've tried various products over the years, most of them not working all that well. My goal has always been something that's tough, waterproof, thin, folds or lays flat in a camera bag, attaches to the flash easily, and, most importantly, works. Here's what I currently use.
The Sunpak DFU-01 Diffusion Kit. Two sizes included, tough plastic/vinyl, waterproof, thin, folds very flat, and good light output. These work especially well for closeups or macro, with the larger one also fine for casual portraits.
Sunpak | DFU-01 Diffusion Kit | DFU01 | B&H Photo Video
The Precision Design Bounce Reflector. Tough plastic/vinyl, waterproof, thin, and opens to lay paper thin in a camera bag. This one works very well for overall scenes in crowded spaces, such as news coverage, candids at parties, or similar events.
Amazon.com: Precision Design Bounce Flash Reflector for Canon, Nikon, Sony, Pentax and Olympus Electronic Flashes & Digital SLR Cameras: Electronics
All of these quickly attach using standard velcro strips. While these will work equally well indoors or out, I also often simply use standard bounce flash indoors. In the end, nothing beats a really large surface, like a wall or ceiling, for spreading out light. But these devices are useful when the wall or ceiling is colored or not refective enough, or the object is small enough to not truly warrant a really large surface.
So what common products didn't work? The LumiQuest products are made using very thin plastic over thicker cardboard. The cardboard prevents them from folding truly flat and the thin plastic doesn't hold up well to repeated use (rips or tears along the folds). I also didn't like the large, billboard-like, "LumiQuest" logos. But, moreover, the plastic surfaces are too shiny or glossy to truly spread the light. The Precision Design reflector above is better in every regard.
The StoFen devices, and variations like cloth socks or the lightsphere, don't do much when aimed directly at the subject (nearly same size as flash head) and require a nearby surface to reflect indirect lighting back onto the subject. As a result, they're nearly useless outdoors and don't really do that much more than standard bounce flash indoors. All three devices above work better overall than the StoFen or StoFen-like devices.
stewart