This book teaches you one single principle effect, and that effect alone is worth the price of the book to me. It goes on to teach several things you can do with this new principle and how you can use it for a book test and even a stab roulette type of effect using no gimmicks (though the spectator MUST follow your directions exactly or it will end very badly for you).

This is a thin book and you'll have to decide if the principle is worth the price or not. You can apply it to any size crowd as long as you have at least five people to work with for the main stage effect. For the variations, you can even use the principle for a single person if they can follow your instructions. Really, this is something you learn and have to really craft to your own performing style, like someone teaching you a double lift for cards, and then you taking that to create your own tricks.

I'm sure this has been taught somewhere else, but I love this wonderfully impromptu piece of no-prop mentalism and I'm glad I bought it.