I heard many people who took EK or used EK material to study say that "EK only covered the stuff that will be tested and nothing extra". How did you know? Were you studying EK material knowing that Kaplan/PR taught more material but were confident that what you were studying was enough? No doubts that the stuff you weren't covering that you may have with Kaplan/PR will be on the exam. I guess that's pretty bold to assume that EK knows exactly what will be on the test ..
I'll bite. On the August MCAT (as well as a few AAMC practice MCATs) there were a few discrete questions on topics Examkrackers did not cover (did not stop me from scoring well though). On the other hand, the Kaplan MCATs had PLENTY of questions Examkrackers didn't cover and that I hadn't seen on AAMC practices either, questions like "what is hygroscopic" - wtf?!?.
Look, if you're worried about covering every single little detail that may be on the exam, buy a good textbook for each subject (biology, organic chemistry, chemistry, physics). Some people (e.g. nontrads) do that, but you probably won't because you simply don't have the time to study every topic in detail.
That's the same with TPR or Kaplan, they have a lot of details, many of which are definitely NOT testable. And if you're like most people, the more you have to learn, the less you learn about each.
Kaplan/TPR: Cover 100% of the AAMC topics with 80% familiarity = 1 x 0.8 = 0.8
Examkrackers: Cover 95% of the AAMC topics with 95% familiarity = 0.95 x 0.95 = 0.9023
Prep companies say what they have to say to earn money. People who self-study (i.e. with EK) have to justify not taking a prep course. People who take a prep course have to justify $1500. Take what everyone says with a grain of salt, but frankly, those are the only opinions you'll ever get on the matter - if you don't feel comfortable with EK, then take a prep course, simple as that.