I personally wouldnt use the mCat practice exams to study for the OAT. I dont know if your material would be similar to mine (I took oxford), but mCat has alot of passage based questions and requires integration of learned info and info given in the passage to answer questions. The OAT is basically just question and answer. I didnt use anything other than my notes and textbooks from class to study for the OAT... The biggest thing is doing some practice questions to gauge how well you know the material. If you can find some practice exams, I think that would be the most beneficial to you. Go over all the topics that they list are going to be covered on the exam, and you should be fine.
I have to disagree with UABopt, about the test material that they send you. I found the book to be fairly similar to the types of the question you should expect. The only section I found harder was biology, but I also havent done any physiology or anta. The rest of it was pretty similar IMO.