I took the RMC 2 day exam prep class the week before my exam and was able to pass the test and felt cconfident in my answers throughout the exam.
Without the prep class I never would have thought about the question wording in the depth which it is required and I would not have had anyway to know the items that are not in the PMBOK… and what the right answer was. As an experienced PM, the course helped me to not think "real world" but instead think "PMI world".
I do not think though that these courses should be used to just get your education and to pass the test. I went into the course having already read the PMBOK, worked in project management for 7 years, and took PM classes as part of my undergraduate degree. I was well prepared before taking the class and the class was there to give me the confidence and teach me the "PMI-isms".