Funny thing, this is more a book that can be seen as a handbook on how to conduct Workshops, but I expect that it can re-used to do retrospectives for the Agile community.

Truth to be told, this is a common theme in this community, they believe that no-one will detect that they are using old stuff or re-inventing the stuff, as long as they re-brand it.

That said, for a Workshop guide, it is OK.