The Tome of Misinfomation it the W&W official strategy guide. It is filled with errors. I own one so I should know. It does prove to be helpful now and again but it is far from being that useful. Unless you could pick it up really cheap, I don't think it is worth the cost.
You get much better information on this board than you will from that guide.
To give you a classic example: The map for the Serpent Temple elevator maze is repeated in a section for Skull Castle as the maps for that area. Obviously very wrong!
Explanations for various things are not necessarily clear. I can look up all the traits and skills in it but it doesn't always tell you how such things are obtained which is why we still have the thread going on the board trying to discover how/if.
Wyv