It's always fascinating to dip into a book of French/English idioms, finding some surprisingly similar as opposed to others which are quirkily different. Why, for instance, is "knee-high to a grasshopper" the equivalent of "haut comme trois pommes"?
With a continually changing language, there is, however, the practical problem of including and accessing easily all the idioms in use. To be fair, this book is quite good at covering traditional idioms of the "butter wouldn't melt in her mouth" or "butterfingers" variety. Yet, when I looked up "cool" or "heels" in the main text or the index, I did not get "to cool one's heels".
So, despite being a little too thick to handly easily and including a rather tortous double method of finding key words, both in alphabetical order and via an index for each language, the book seems a bit "hit and miss" and arbitrary in its selection of idioms.
When I tried to look up a series of idioms I have learned recently from the French TV news (Le 20 heures), I was often unable to locate them in this book e.g. "mettre à l'index" which means to blacklist or boycott, or "avoir le moral en berne" which is to feel downcast, as when a flag is at half-mast. This suggests the book may not reflect current French language "as it is spoken".
I think that online searches of idioms are more likely to yield results quickly. Idioms are probably best absorbed "in context" with a computer on hand to check them out, but I suppose there's no harm in using this book for an occasional browse. Perhaps 2001 idioms aren't quite enough!