Here's my concern about the Fong. If you point your flash straight up to bounce it off the ceiling (with the fong attached) you're going to waste your flash's power. You're already losing about a stop of light from the fong, and you're going to lose more when it diffuses your light in every direction - including behind you, to your left, to your right - literally 360 degrees.
If you bounce your flash, I'd suggest making a bounce card that attaches to your camera - the card will at least throw your light forward to where your is subject instead of behind you where your subject is NOT.
I personally think it's just a waste of money.