I very much enjoyed reading this book. However, I would have to agree that it is only good if you are going to go on a trip to Scotland (which I would definitely recommend!)
The basic haunting history of each site is good, although I personally would have like more information simply because it would be more interesting. One thing that did put me a little off was the mixups in some of the historical facts (twice in the book the author called Lord Bothwell, who married Mary, Queen of Scots, by his real name, James Hepburn, which is correct, but under Crichton Castle, the author calls him Patrick Hepburn, and the author spelled people's names wrong or differently, sometimes within the same sentence. Minor details, doesn't really take away from the book, just irks a historian :) ) but other than that it is a good book.
From my own experience in Scotland, most places that appear to be on private property are best viewed from far away, and when in doubt, just don't go up to them. If there is someone you can ask by all means do so, as most people won't mind so much in Scotland, but otherwise just use your judgement. Also, those that are said to be in a dangerous condition, they can be visited, but from personal experience be VERY CAREFUL (I almost got hurt at Duntulm Castle, could have been my own clumsiness but it is also a very ruined castle).
Great book, but with more info I would have given it 5 stars.