Few people have anywhere near Jeremy West's playing or teaching experience on the cornett/cornetto. He writes clearly and practically for those making first sounds, going through warming up, playing long notes and then cooling down. The importance of playing with a tuning metre is stressed.
There are many exercises of somewhat progressive difficulty for acquiring fluency of fingering and building embouchure to play progressively higher notes.
What the book lacks is a genuinely progressive "learn as you play" approach, and it assumes the player is an adult learner, already experienced with notation and how to practise. Although the exercises are progressive, there are notes on the first page of "beginner" studies and warm-ups that may not be playable for several months by a beginner, which the writer understands and expects the reader to select from appropriately. To make best use of the book, you either need to be able to structure your own learning, or work with a teacher who can do this for you, as the book does not focus on giving that structure.
A reader who values a no-nonsense, rather austere, "do it the shortest, steepest way" will love this book. There is little attempt to provide "tunes" to play for the enjoyment of playing the instrument, but there are lots of very systematic exercises.
Overall, the book gives a wealth of components for a self-motivated and resourceful learner - and since the cornetto is a very steep mountain to climb, why would anyone be reading this book who is not self-motivated and resourceful?