The RYA YM scheme offers a quite unique and experience-based way to acquire internationally recognised sailing certificates. I myself have purchased and thoroughly studied this book as I - having a German sailing background - wanted to familiarise myself with the British syllabus and exam requirements.
The book is very well written, concise and comprises all important aspects of the RYA syllabus. However, further additional reading on some more specific topics such as meteorology, the IRPCS or terrestrial navigation is certainly advisable, but couldn't be expected to be covered by a book like this anyway.
I have found a few comments of other reviewers complaining about the author's writing style, saying it was self-indulged, old-fashioned and incomprehensible. Perhaps the reviewers made particularly bad experiences with Tom Cunliffe as a YM examiner, tend to polemic comments in general or lack some experience.
Given the fact that I as a non-native speaker had no problem at all to understand this book (and I certainly have when it comes to historic logbooks and letters) I find it hard to believe that there should be anything old-fashioned among this book. The entire concept of the book has been rather further developed and adapted over the years in quite a few new editions, making this book an inexpensive and up-to-date compendium.
The odd salt-dog-talk is certainly sometimes unfamiliar, but not inappropriate or cryptic, quite likeable and rather entertaining. Whoever has seen Tom Cunliffe on TV knows that this is rather his personal style and should not be interpreted as self-obsessedness.
The drawings and pictures are very didactical and useful and straightforward to understand and work with. The book leaves little to be desired for. A sort of hightlighted keywords in the text or on the margin could make it easier to find certain text passages. Ten pages of weather related content is unfortunately rather a short sketch of a summary if any at all.
I would absolutely recommend this book together with Basil Mosenthal's 'Learning the Rule of the Road' and a book on meteorology (sorry, only German recommendations here: Seewetter, DSV-Verlag).
Fair winds.