The strength of this book is twofold: first, Cheng has brought together both positional and directly tactical exercises under one cover; second, because he's grouped them randomly, and with wide-ranging levels of difficulty, it creates a situation akin to 'thinking over the board'.
I have not found it easy, and that's why it's been so rewarding to work with.
This book will likely be helpful to all class players, and a careful study is sure to greatly benefit your game.