Jim Harmer of Improve Photography conducted an interesting experiment in which he stacked the Gary Fong Lightsphere up against an ordinary piece of tupperware:
The Gary Fong Lightsphere costs $50. For a hunk of rubber that produces only marginal improvements over the on-camera flash in my opinion, that is just way too much money. The fact is that the darn thing looks like a piece of tupperware to me. So, I got curious. Was this product doing anything that any other hunk of plastic couldn’t do?
His conclusion is that there was absolutely no difference in quality, and that you should save your money by using a makeshift diffuser.
Gary Fong Lightsphere vs. Tupperware [Improve Photography]