This book is really good. It gives an "idiots guide" to the levada walks, including some limited (but helpful) commentary on the plant life, architecture etc. The grading are helpful and the maps at least provide an overview of the routes.
Two pieces of advice, however:
1) The Madeiran/Portuguese government are currently renovating the levadas (2009-2010). For example, in August 2009, we turned up to the the Levada Nova route in this book only to find a 6km stretch of it is closed until Feb 2010 for repair. Based on this, I would always check with the Madeiran authorities what is open and what is not.
2) The book is good, but it's no substitute for a proper OS map. Inevitably, there are diversions due to maintenance work. The route descriptions in the book only work if you follow them perfectly, and the maps aren't detailed enough to be able to track your diversion and re-join the main route later. The book takes the hard work out of map reading, but I'd always still take a map just in case!
All together, worth having and definitely enhances the experience of our walks, though,