Chambers is the leading name in reference works in the UK, and so it is not surprising that this is an excellent work. The question is do you really need a biographical dictionary? Just how handy is it, and does it contain the names of people you might be interested in?
I got along without one for many years, but I find it increasingly valuable not only for my reading and writing but for following the news. I use to look up spellings in the back of my Merriam-Webster dictionary (one of the uses of a biographical dictionary), but found that only worked for really famous and usually dead people. Now when a newsworthy person is mentioned I can look that person up in the Chambers biographical dictionary and usually find an entry. Even if that person is not found, at least I know that he or she is new to the celebrity game.
Let's check some names and see. Osama Bin Laden? Yes, he is found under "Bin Laden, Osama bin Mohammad," born 1957, "Saudia Arabian terrorist leader." He gets about 250 words. His near exact contemporary on the next page, "Bird, Larry (Joe)," born 1956 "US basketball player" gets about 90 words. Between them I find "Binoche, Juliette," born 1964 "French actress" with maybe 80 words.
Well, what about, say, the Buddha? Yes, he appears and gets a special text box as befits "the enlightened one." (Jesus Christ, "believed to be both human and divine," gets a bigger box.) Others getting boxes are poet T.S. Eliot. He gets almost as much space as Jesus. And Queen Elizabeth I, etc. Shakespeare tops them with two big text boxes.
What about the possible UK-bias in the selection of names? There is a slight bias, but remember Chambers wants to sell this book not only in the bigger US market but to English-speaking people world wide, so the bias is kept to a minimum. One thing to note is that your run-of-the mill US congressman is not listed. Orrin Hatch (long-time Republican senator from Utah) does not appear, but the late Strom Thurmond does. Of course President George W. Bush does appear, but embarrassingly enough (embarrassing for the precognitive powers of the editors, perhaps) Massachusetts Senator John Kerry does not appear.
Scientists are not neglected. There's a box for Stephen Hawking, for example, and biologist Edward O. Wilson gets a mention. Even literary critics appear, the late Edmund Wilson, but not Harold Bloom. Speaking of blooms, Judy Sussman Blume, "US writer for teenagers" gets a hundred words, but US writer for adults, Howard Bloom does not appear.
Una McGovern, who is the editor for this the Seventh Edition, writes in the Preface that the criteria for inclusion is the same as it has always been, "achievement and recognition" while hinting slyly that "recognition" is probably the more important factor. There are "over 17,500 biographies" stuffed into 1,650 two-column pages. The book weighs about five pounds so it's a little bit of a problem for extensively perusing while in bed. Every edition adds new celebrities, so some old ones have to be eliminated to keep this to a one-volume work. There are about 500 new entries for this edition including Madonna (the new one, not the old, although "Mary, Mother of Jesus," does rate one and a half column inches.) And speaking of Biblical comparisons, I recall that the Beatles had remarked some years ago that they were more famous than Jesus of Nazareth. Let's see what Chambers thinks: Well, the Beatles do get a 700-word box, but Jesus gets one twice as large.
Bottom line: more entertaining than one might expect (but this is a Chambers reference book trademark--see their quotation books), and definitely worth the relatively modest investment.