While I have never used examkrackers, I did use Kaplan (classroom based) and was very pleased with thier results. Their resources are unlimited as well. I too found that the best way to study was by doing questions and reading the answers to the ones I got wrong or guessed at. I took Kaplan's course twice (took advantage of their higher score guarantee since I wasn't pleased with my results). My first diagnostic was a 14
and I got a 21 on my first official MCAT. I was disappointed, took Kaplan again along with some other classes and I ended up with a 28 on my second MCAT. About 2-3 weeks before the 2nd MCAT, all I did was questions, questions, and more questions and that made more of a difference than anything else. If you use Kaplan, Princeton, EK, try to do as many ?'s as possible, along with solutions, and things will make sense.
Other than that, relax and good luck.