I am just starting to research independent schools for my year 2 son, who is currently in an excellent state primary. Our local secondary schools are not so good, and so we are looking at private prep schools from age 9 or so, then moving on to independent secondary school. The book is a huge tome (1463 pages), and has proved a superb resource.
It does not cover all schools. Not even all private schools. Those that it does include (around 1000) are mostly very comprehensively detailed, but I was disappointed that 2 of the schools I am very interested in (both of which are generally very highly rated IE 'Good' schools) are missing. No state schools in our area are listed at all.
There is a great deal of excellent general advice in the introduction, about how to go about choosing schools etc including lots of invaluable info about how the system works.
All in all, a highly recommended book primarily if you are looking for an independent school, but you will need to read elsewhere as well. It is of limited use to those looking for state schools. A good investment for me, I think, but I do wish it was more comprehensive.