Useful for middle grades, because of the content, illustrations, and index. Also good as a way of bringing in historical information under the guise of "ooooh, pretty things."
Would definitely recommend for "interesting" non-fiction.
A pretty enough book written not quite as a history of the times, not quite as a history of Febergé, not quite as an art book and more of a book for older kids than for adults. As an adult I wanted more history, or more biography, or more art so skipped through this in an hour.