Admittedly, I am somewhat biased toward this author as I enjoy "Ground Force" more than any other home improvement show and have converted several friends from HGTV over to BBC America.
The plans and designs are honest. They clearly outline how much time it will take, the safety aspect and estimated costs (In british currency). I have noticed that her costs seem a bit low, but it may be the geographic differences. Mostly, I use this on a relativity scale. (This pond is more difficult/costly than that one)
She shows wisdom and experience in her discussion of the use of native plants and introduction of wildlife. Unfortunately, there is a bit of difference between Los Angeles and London native plants, but if you apply the general idea, you can't go wrong.
The practical ideas, like: "Don't put a fountain in a windy area" or "How to hide the pipes in a wall mounted fountain" are essential things to think about once you have it your head that you must have a water element in your yard.
My husband owns a landscape design company and he frequently uses her book to narrow down a client's broad vision. A great garden library addition for a professional or an amatuer!!