This is a fine guide indeed - it covers more non-US artists than some other notable editions (European, Azian, African artists...) and it really tries to keep up with recent developments in jazz.
Naturally, all that means that traditionalists might desire larger articles on (mostly American) true jazz giants of the classical era, but that's just a matter of personal taste.
Some of the articles are impressionistic, unneceserily pointing out that an artist didn't play so well when he wisited Europe few years before he died, but failing to say why precisly was he so great, but most of the articles are (in the worst cases) fine, written with real passion for the music, and often relying on serious research.
As a fan (primarily but not exclusively) of older jazz I'd like to point to the articles on Buddy Bolden and ODJB, where the influence of this all-white group's influence on British society is comparable to the influence of later punk musicians (!?).
So, this book is not only interesting and useful, it is also thought-provoking.