I really like these travel guides, for someone on a reasonable budget and interested in cultural and other standard "tourist", including walking, shoppping, eating/drinking out, etc and even business travel.
Generally, I always buy one for the country/city I am going to visit. When I don't have one, I usually regret it as I find I am "lost" without it in terms of planning what to do and how to do it!
They provide interesting and practical facts about sightseeing, using the local public transport or driving, getting to/from airports, eating out, going out, shopping, useful maps of city centres, health and safety tips, some background history, etc.
The translations (and pronunciation guide) of common phrases in the local language are useful but sometimes limited. Lots of colour pictures makes the book more interesting in itself and makes for a nice bookshelf souvenir afterwards.
Another great thing about the series is that the books are always laid out in the same way. So once you start using them, you'll always know what information you can find and where it will be in the book.
A slight drawback is that the books are medium-size and can weigh from 500-800 grams (depending on which city/country the book is for), and the paperback versions always get a bit dog-eared being carried around in my day-pack.
To paraphrase and old credit card ad: "I won't leave home without one of these guide books".