Anyone ever used them? Are they worth investing time and money on just for straight up content review?
content books, 6/7 out of 10. They are black & white, huge, not very pretty or efficient
The only reason I give them a score > 5 is due to the sheer # of practice questions and passages in the book (~ 700 per book IIRC) which makes them useful. For pure science I'd go with TPR or EK.
The next step strategy/practice books and Q book are great though, so I would say to get those. they have an entire CARS books with 108 passages and explanations.
There are so many good or decent/free resources for learning science, I would really only use the prep companies for just that, prep, meaning practice tests and practice materials.
content review is the one of the least important parts of your mcat studying. you need to see the science from the way the aamc tests it early and often, and then review your mistakes. This is why I'd would say if you are going next step, get their Fl exams and strategy/Q books. the explanations are among the best out there so often you do not need to go back to your notes.
For pure science, grab tpr, or ek. (tpr is great for psych/soc especially)