Well, I bought the Stofen omnibounce. I DO think that it's ridiculously overpriced. I DID consider to return it back to the store. But then I noticed its effect on the White Balance and I decided to keep the diffuser. The walls and ceilings in my apartment have yellow tint, so in my case the effect on the WB is quite significant.
So, as you can see, I have mixed emotions on this subject. You should keep in mind that in any case the difference won't be that great and it will require a little bit of practice to learn how to get some gains from the diffuser.
Some people say that Lumiquest is more efficient. Some people even report that they can achieve a studio light effect. I don't have Lumiquest system (yet
) But, judging from the pictures, the omnibounce is easier to handle.
So, if you have extra $20 then try it. If you don't like it try to send it back to the store (or keep it just in case, but don't tell anyone you've wasted $20 on a plastic cap )