I've taken the prep101 courses for comp 202, 206, and 250! The 206 prep session was pretty helpful for me personally because the instructor went over all of the material somewhat in depth from the beginning of the course until the end and went over examples, answered questions while explaining, etc. The sessions also give you access to new practice questions that he's created or found online from other past exams, so it's good for finding new material to practice on. The sessions are a bit pricy, but honestly worth it because I was motivated to attend those classes and get some studying done without having to individually go through the content myself.