Thought on The Cambridge Companion to John Cage

I am considering purchasing the Cambridge Companion to John Cage
(Edited by: David Nicholls) as a gift for someone who has read most of
Cage's books, Kyle Gann's book on 4 33 and James Pritchett's Music of
John Cage.  Thoughts on the quality of the Cambridge Companion as a
supplement to those books would be appreciated.

Thanks