I bought this when qualifying as an ETM teacher last year. It's really good from an aerobics point of view, and was incredibly useful - lots of parallels with my training course (YMCA).
However, having since qualified as a step instructor, and revisited the section for step - it's left me slightly concerned. Key teaching points are missed, and the choreography samples are confusing. I'm not sure that you could use this section to create a safe and effective step session, especially not one aimed at anything higher than complete beginners. Ditto for the weights sections - it's trying to cover a big subject in a small area, and doesn't quite get there. It's probably good as a general overview of what you should consider for each of those class types, and good as a reference if you already know what you're doing, but I'd be cautious of assuming that once you've read this book you'll be able to teach those class types.
GREAT for aerobics and body-weight MSE. Shame it didn't stop there...