Yeah, I think they are pretty close to the real deal. Don't forget to check out some of those retired Step 1 questions (I forget the website). Those questions have a slight tendency to pop up again on the boards.
I took the Kaplan test several years ago to decide how much studying was required to do well. I took it, did well, didn't study, and scored within a point of my Kaplan score on the actual exam. I think the pre-test is purposely more difficult, to convince you to take their course, and then the post-test is not as difficult, to convince you that you learned something from their course, and then you do about the same on the MCAT to prove its veracity. I only took the post-test, but talked to people that did both, and that was my impression. It should be noted that I am a cynic by nature.