Strengths: Explains in good detail the basics behind HRM and directly addresses the skeptics. Light hearted manner makes for easy reading.
Weaknesses: Some silly spelling mistakes and typographical mistakes detract somewhat. Also, the suggested training plan is quite heavy - running for 6 days out of 7 - not something I could manage personally.
Overall: Using the advise in this book (but NOT the suggested training plan!) I spent six months training for a Half Marathon. I achieved a PB on race day, knocking 14 mins off my previous best time and achieving a personal goal of getting sub 2 hour. I've no doubt that the information given in this book worked very well for me, as it's taught me to use the monitor to run at an even pace during racing as well as using it to best effect during training. I would recommend this book.