Some of their tests are much much harder than the real thing but others are closer to the real thing, so it depends on which test you are talking about. Also, certain sections in some of the tests are close to the mcat while others may be much more difficult. For example, the verbal of one test may be reasonable but the other two sections would be much more difficult than the real thing. I personally scored about five points higher on the mcat than any of the berkeley review tests, even the easier ones and even the ones that I took at the end of the course! Again, the AAMC are very reliable and good predictors.