I did all 9 of the BR exams and most of the AAMC exams and found both useful for different reasons.
For the AAMC, I felt the timing was close to my real MCAT, but that the passages and questions on my real test were harder. I thought my verbal passages on my actual MCAT were longer than AAMC and had more inference questions (my nemesis). The PS passages were good, but I thought the questions on the practice exams were easier than my real exam. I always finished my practice exams fifteen minutes early, and that wasn't the case on the real thing.
The BS sections were generally good. What I liked is that they were so random in terms of what they focused on. It made me realize that the MCAT could cover pretty much anything they wanted. I'm definitely glad I did AAMC exams to get an idea of the timing and writing style. I did about four points lower on my AAMC exams (average score) than my real MCAT.
For the BR exams, I agree with the previous posters about the VR scale. It was too generous. I was getting 11 and 12s on BR and got a 10 on the real thing. I liked that the passages were long and boring, because my actual MCAT had all long, boring passages. But I didn't really like their questions all that much. I don't remember much about my real exam or BR exams in terms of VR, but I do recall thinking that the actual MCAT was a bit easier to use the passages for answering questions.
BR PS was perfect in its weirdness, difficulty, and doability (not sure that's a word
🙂 ). I felt that BR prepared me better for what to expect on my actual MCAT PS than any other source, including AAMC. They had calculations, experiments, and bizarre stuff just like the real test. I was getting 12+ on BR exams (much to my surprise at the time) and ended up with a 15 on the real deal. I can't say enough about how well BR did with PS.
The BR BS sections on the exams are really good, better than the books I thought. They are hard, but so was my MCAT. I liked that some passages were straight forward and you could answer questions by applying the passage information directly. I also liked that some passages were crazy weird and made me stop and reread, because I had a couple of those on my actual MCAT.
All-in-all, I felt the BR CBTs prepared me quite well. I also think everyone should take AAMC exams. It shouldn't a one or the other choice. Do both!