Well, first, the original Fitter U was only 12 weeks long and developed exclusively in MP3 and PDF format.
Fitter U Fitness, the sequel to Fitter U, is a monthly membership program that provides you with new and exciting athletic workouts in audio, video, and PDF format. As a member, you also have on-going access to the "Locker Room" forum for all the assistance and social support you could want.
These elements were not part of the first Fitter U program. Furthermore, Fitter U Fitness is slightly more advance (yet appropriate for everyone except absolute beginners), more time efficient, and has been developed to produce even greater results than its predecessor!