Flash diffuser - do you use one?

I recently received a FL600R. I saw the suggestion for tapping a 3x5 card to the flash as a diffuser, but was wondering:

a) do you Need a diffuser?

b) Rogue Flash bender - Large or Small

c) is a comercial difusser like the Flash Bender "worth" the $30 cost?

Thanks

My primary use of the flash is to shoot flowers, butterflies, and a small coin collection