It's also far more attractive then the MBox AND the Firepod. If you're into a nice looking rack with quality, affordable inputs, go for the 400f.
One thing to look out for in Sonar 4 Producer Edition (havent tried it in 5), however, is an interesting effect where the last tone played from a track is kept in some sort of irritating loop until you either rewind to the beginning or go into options > audio > advanced and make sure "play effect tails after stopping" is checked. That is one problem I've never had using any other interfaces with Sonar, and is easily fixable.