NAUI's "Master Scuba Diver" course is a course by itself and isn't a mere take five specialties and get an "MSD" certification card. It entails a great deal of in class academics at "instructor" level knowledge in diving physics, physiology, decompression, equipment, etc. There are also openwater dives required (at least 8 dives). Graduates of this course should have academic knowledge and open water skills that are at an instructor's level (without the teaching skills) at the end of their training and certification (in-class exam and in-water evaluations are required for certification).
It is probably the most challenging and most knowledge and skill intensive course in recreational diving. NAUI requires this course and certifications as a prerequisite for ALL of its leadership (AI, DM, SDL and instructor) and technical diving programs.