If you get this book, then you won't need to get Feng Shui Demystified I, as this book simply is a more comprehensive version of that book. In addition, you can get this book for much cheaper if you are willing to just get it in pdf form (it is sold in other places on the web).
I will say that with the typos, and the fact that the author's native tongue is not english, and also with all the different formulas that sometimes intersect with each other and what other books say, that this will be a confusing experience for some people who study flying star feng shui. For example, his notation for mountain/earth/water star is like this 2/5/8. In other words, you have to hunt around the book to see which number goes to which position. He also says in many sections that if water comes from this direction, then it is auspicious. Does that mean that the water goes toward the direction from an outside location, does it mean that there is a water feature there, or does it mean that water originates there and goes in some unknown direction? This is not made clear. In addition, I read the castle gate formula in the book several times. Despite reading it several times, I could never understand how to replicate the formula on paper since his explanation was so terse. The formula is in the book, it's just that I don't understand it.
Still, his book is the only book in which I've seen certain formulas written in english, and for this reason, I would recommended it if you are an advanced learner for flying star feng shui. It would not be my #1 pick for a flying star feng shui book, as I do not agree with some of the formulas/methods in written in the book based on personal experience.
The idiot's guide to feng shui second edition is the best feng shui is still, imo, the best flying star feng shui book out there (I've only read about 15 books on feng shui so far though...) and if you are on a limited budget would be the book I would recommend. I've had the best success following the flying star feng shui advice in this book along with some feng shui advice from non-flying star methods (such as those books from Lillian Too - although her methods are hit and miss).
Feng Shui Demystified will get you thinking. I wouldn't say that it demystified feng shui for me, but it does make you think and question about different methods as well as try and experiment with them.