This is a book I've taken up and put down several times. Along with a small group of pastoral supervisors, we've discussed it, a chapter at a time. So in a sense some of it's been read more than once.
There are bigger books on supervision around, more complicated ones, and ones that seem more erudite. Leach and Paterson's book is the only one I've come across that approaches the subject from a Christian perspective, and since the group I'm involved with are all Christian supervisors, this has made it all the more valuable to us.
Not everything about the book works: some of the anecdotal examples don't always seem to work as good examples of what's being discussed. But overall this is a very helpful textbook and our group could productively work its way through it again.