No harm getting one to try. You're thinking of what? Gary Fong's Puffer? But I predict that you'll get mixed results.... because I used to have one of these things. But a bounced flash works so much better
In a large hall, the ceiling may be too high to bounce a flash even at full power so a diffuser/bounce flash card is required. But in a small room, a bounced flash can work just nice for a great effect. If your friend has a bounce flash compatible with your hotshoe, you may want to borrow it?
Sorry if my reply came too late... coz the reunion dinner is probably over. If so, wanna share about what you did? Happy CNY btw!
Guess you could still stick to your onboard flash if not too much trouble. A diffuser may or not help you attain your desired effect. It'd definitely cut down on the power of your flash. Why not try it out at home with under simulated conditions and see if it's what you want? Personally I would go without it.