Hi Rene,
JAJ has held various hats. A clinical Daoist, Daost Sorcery, Daoist Philosophy - various aspects and has books for any hue and flavor one would want.
This book is pretty dense and useful if you are already familiar with the subject. If you are new, I would not recommend it (a lot JAJ’s books were written as textbooks for his students).
When I first read his books, I was initially turned off but when I personally met him, I was amazed at his practical attainments (I don’t say this lightly having met many famous and infamous Daoist teachers). My interest has mainly been in Daoist Sorcery (it does not mean the negative Western connotation associated with the word sorcery) and medical qigong aspects - and he has 5 wonderful volumes on it which are used as textbooks in several alt medicine colleges. I don’t seem to have this particular book in my collection, the one you mentioned (or may be I do, I will look again haha)
Concepts are useful as are books. As we say in rDzogchen, the right view alone produces the right results from any practice. A practice, devoid of the right view, produces deviations. So, it is important to have a firm understanding of concepts. The very fact that folks assume that Daosim is all about techniques and cultivation is in itself wrong because pure philosophical schools of Daoism do not practice any techniques - what to practice to realize what is already known? And there are cultivation schools that emerged after the original Daoist schools, with a good amount of influence from Indian Buddhism and we now have the current cultivation-centric Daoism.
All that said, given its price, I would say proceed with discernment. Also, if I happen to find it at a cheaper price anywhere, I will message you (I am always on the lookout for rare editions).
Good luck on your amazing journey!