Honestly, the main takeaway from this is that the rich will do anything to stay rich, even if it means putting other people in the worst working conditions humanly possible. There are patterns that repeat themselves throughout history, and the way that Mann breaks this down is fascinating. 

The overall tone is accessible to teens, I think, written in a way that's easy to follow. The labor movement in the US isn't one often covered extensively in US history classes (with the exception of a few major events), and this is a nice supplement to that. Overall, really well done, even if it might not be the most popular subject for teens.