I can't say how well this book works for complete beginners, but I can say what it did for someone who had been gradually learning to do cryptic crosswords for about 10 years. When I read it, I could finish or nearly finish the Guardian and Times puzzles I was tackling but being self-taught, I sometimes solved clues without understanding them properly. This book (first edition) clarified my understanding of clues, and gave me the confidence to start tackling harder puzzles regularly, and to enter the Times Crossword Championship a year or two later. Three years after that I reached the National Final for the first time (1992), and on two later occasions I walked away with the trophy.
Other ways teaching may suit beginners better, but some of the criticisms in other reviews are just plain daft. To the person who complained about untaught indicators in test puzzles, I can only say that untaught indicators are what you have to deal with in real puzzles - learning to solve by rote is not a good way. Likewise including clue types previously learned in test puzzles - you have to learn to see what type a clue might be, not just to solve it when you know the type already.
Declaring an interest: I know Don Manley personally and he recommends a website of mine in the book.