Excellent course

Strengths:

The site allows you to understand the subject in detail and then to do exercises for each chapter.
Very complete.
A schedule is made to achieve your goals.

I recommend the site because it is very organized and complete. I think that it is important to follow the schedule and to have time to prepare for GMAT. Personally speaking, I first read all the chapters and then I did the exercises. I also did 1 GMAT mock up test per week the last 3 weeks before the real GMAT.
I also used the personal test that everybody can take at the site. It is interesting because people can design their own tests based on their weaknesses. Here, I selected all hard tests to practice on more difficult exercises. It is important though to do that after you master the easy and medium exercises.