Manhattan GMAT is the real deal. I took the 9-week classroom course and scored over a 700, after beginning in the lower 600s. The class instructor was informative, motivating, and very clear in his explanations. The 11 or so books help greatly and ensure you will have seen practically everything on the test before - except for select 700-800 level questions. The recorded classes available online help greatly when refreshing your mind in the final weeks before the exam. Not to be underestimated, there's also a study guide that tells the student exactly what to study, when to study, and how long it will take to complete. This helps to keep you on track and not study too much on one subject area.
The course is NOT for the unmotivated. Depending on your test date, you can expect to put in 15+ hours a week if you're taking it within 3 months (9 week course + 3 weeks of post-course study) . That comes out to roughly 3 hours a night. If you want to go a bit slower, they advise 7-10 hours of study per week.
As the course progressed, pre-class discussions suggested many students struggled to keep up with the course load and complained of lower than desired practice test scores. I later heard a number of those students failed to hit their targets on the official test.
Manhattan GMAT provides free, weekly 30-minute calls with instructors to work through problem areas. This perk is known to be underutilized, yet is extremely helpful and, in my case, provided me with guidance on how to answer a couple challenging 700-800 level questions that ended up appearing on the official test.
Manhattan GMAT is for people that want to get a high score, want to get into a top tier school, and are willing to put in the effort. Also, MGMAT hosts frequent free courses by mbaMission to help with your MBA admissions process. Between MGMAT and the free courses, you really don't need anything else to get you into a great school. It worked for me.
Pros: Great Study Materials, Instructors, Practice Tests
Cons: Time consuming