So I made a couple of these last night. Initially I made them too big, and had to cut them down, but even so, they seem to put a
lot of light forward.
I kind of envisioned them adding a nice soft fill light, but in reality you end up getting more light from the card than from the ceiling. There's a simple reason why: the light that bounces off the ceiling has to travel farther to reach the subject than the light that bounces off the card, and the inverse square law says rears its ugly head.
As such, I don't think I'll want to use them on my flash while it's on the hotshoe, but they'll probably be pretty good for using off-camera in cases where I don't have my umbrella or other diffusers with me. I also used some of the leftover foam to make a smaller bounce card that's just the width of the flash head and extends about 3" above it. Index cards work just as well for that, but this looks nicer and might last a while.
Here are some samples, all shot with the flash in TTL mode. Look at the reflection in Santa's right hand and foot to get an idea of what the ratio of the light bouncing off the ceiling to the light bouncing off the card is.
On camera flash (SB-600), bounced off ceiling:
w/ small bounce card:
w/ big bounce card:
w/ dome diffuser (in this small room, almost no difference between this and the small bounce card)
off camera w/ big bounce card (manual flash power for this shot):