I don't know much about the formal post-bac. programs but some SMPs require a MCAT score to apply. If you do take the MCAT prior to the SMP, as mentioned above, definitely make sure you can dedicate ~2 months (at least 2, depending on your base knowledge) for study/taking the exam. In addition, if you take the SMP, make sure you're ready to bust your a**! Most are not easy and mimic a year of medical school! I think SMPs can definitely improve your chances of MD/DO acceptance if you crush it, however!