I would also say EK is mainly for reviewing the material. Although I did well in my pre-requesite courses, I felt like I was reading someone else's notes as I was going through their book. As a result, I only ended up using their O-chem book.
I would also believe it depends on your personal preference and basic understanding of the material. If you have a solid understanding of the material, I think EK is a great book for reviewing the key concepts. Unfortunately, most average students like myself aren't so used to learning the concept that MCAT stresses, so I had to re-learn the material basically from scratch.
Good luck.