I heard a lot of good things about Demb Flash Diffuser Pro and like to compare it with Gary Fong's Lightsphere Cloud.
Test photos are shot with D700 SB-900 manual and manual flash mode.
First Test: bounce with a 30 ft ceiling.
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Second Test: bounce with a 10 ft ceiling.
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I think Demb Flash Diffuser Pro does a better job on saving flash/battery power and offers more versatile in your camera bag. However, if location has a low ceiling then lightsphere will do a better job.
Happy Shooting.