imo, these cd's are a good REVIEW of what you already know. So if you're gonna buy it for that reason, then definitely go for it, but I wouldn't depend on it if you hadn't already tackled the subjects through books first. A lot of things may not make sense otherwise, or they may appear to be going too fast. As for me, these cd's have helped me build a stronger foundation in the sciences & cleared up a lot of things I was always wishy-washy about. They explain a lot of concepts really well, and encourage you to think more intuitively, which will definitely help when you tackle MCAT passges.
No doubt, the convinience factor is probably the biggest advantage you can get out of these cd's. If you don't end up finding these cd's very useful, or if you don't need them after you're done using it, you could always get some chunk of your money back by selling it on ebay or something. They seem to sell pretty well.