I bought this book to do some book learning before a diving holiday, hoping it might give me some more background info and be a bit less patronising and American than the PADI handbooks. Although it is written much better than PADI's books it gives only the most basic information. If you have dived before and have some interest in the diving media then there will be little worthwhile information here for you. If, however, you are completely new to diving and want everything explained in one place in a succinct and unpatronising way then this may be a useful book. The seller I bought it from was very cheap and delivered promptly.
A good way to orient yourself in the world of diving but of little use beyond that.