Summary: Just the right size flash when the on camera flash is not enough and a full size SB600 is too much. The SB 400 has about twice the output of the on camera flash yet is small and very easy to carry. The recycle time is very fast, seemingly endless number of flashes on a set of AA batters. The best feature is the tilt up head which gives you the small and convenient bounce flash not available with the on camera flash. It's a lot of flash for not much money.
Pros: Consistent Output, Fast Recycling, Lightweight, Versatile