I bought the two supplements just cause I wanted more questions to practice. The questions are organized like the OG 11
so only the last 20-30 are really challenging. Also, the practice questions that you get for free with the PowerPrep software are from the supplemental questions. If you really want some more practice then buy them, but don't expect too much. I was dissapointed when I got to the PowerPrep software and had repeat questions coming from the supplemental books.
Hope this helps.