The only product I've seen from Hex Games prior to this book was QAGS, but the two are worlds apart. QAGS is a silly if well-constructed system for rapid, rules-light role-play. Magic rules is a comprehensive, in depth look at a fluid and infinitely adaptable magic system for any style of play. If you are looking for a magic supplement to any Hex Games product, this book is for you. If you want a solid resource for modifying the magic system of any other game, Magic Rules has something for you too.
For the low price of "free" there's really no reason not to look it over!