In brief: a solid resource for the beginner swordsman, and a splendid example of a progressive curriculum for instructors of any level.
If you're looking for a general reference/guidebook for Italian medieval martial arts, this is not the book for you. Instead, this book is a guidebook for someone just getting started: a curriculum to work through, chapter by chapter, at the end of which you will have learned all of the basics: blows, stances, and tactics, all the way through swordplay to grappling and counter-grappling.
I found it particularly useful as an instructor, especially since Guy's spent years refining both his interpretations of the sources and his teaching method. There's a lot to learn about how to teach, how to structure a curriculum, and how to get students ready for freeplay, all cunningly disguised as straightforward, easily read and understood instructions.
As always, Guy's language is clear and precise, and contains no small amount of good humour.