This is more a celebration of this particular architectural practice than a practical reference. It's about principles and the way this architectural practice works, so don't expect to learn hands-on conservation techniques from the skilled tradesman's point of view. It's a huge book of 267 glossy pages with some stunning photographs, but I got through it in about one and a half hours and didn't lose anything in the skim-reading.
If you're thinking of establishing an architectural practice specialising in conservation work then it's worth a read (and it'll look good on the bookshelf beind your desk), but for anyone who spends their working day getting their hands dirty - forget it, Bernard Feilden's 'Conservation of Historic Buildings' will be a better investment at this level.