For the MCAT, benchprep is outstanding. But if you're trying to get a leg up on orgo, I don't think benchprep is going to help you much. MCAT orgo is FAR FAR FAR easier than the orgo you'll get in school. Benchprep shines in that it gives you practice problems that prepare you for the type of questions you'll come across on the actual MCAT, but the questions you'll get on tests in class are going to probably be more time and thought intensive, and more straightforward.
If you're looking for a good resource to help you with orgo, I found the "organic chemistry as a second language" bookset pretty helpful. Although, in all honesty, once I started to get the hang of orgo and just had to memorize reactions and mechanisms, the books were less helpful than just taking the time to study consistently.
Good luck!
