For Beginner -- This book basically is the shorter and with more understandable english version of the confusing and lengthy spec. For a beginner, try to read the spec is not very easy. Tis book provides a good starting point. However, this book doesn't tell the whole story, such like the relation between L2CAP channel and baseband channel. The initiator of the L2CAP channel must be the Master of the piconet?? Such confuing concept is not well explained in this book for a beginner and when the beginner starting picking up, he should start finding many such ill-explained (or not explained) concept in this book.
For advanced reader -- This book tells something but doesn't answer the common confusion in the spec. One example is that on p.134, it said the L2CAP_Connection_Request is for a connection-oriented channel and a PSM value is needed. However, on p.130, the connection-oriented PDU, there is no PSM value and PSM only exists in connectionless channel as shown on p.129. Maybe the answer is somewhere in the book but I haven't found it. So in short this book resolves some confusions in the spec but it also brings up more confusions.
Overall, I think this book is worthy of owning and I strongly recommend it to everybody who who wants to study Bluetooth technology. However I don't think it deserves 5 stars as other people have given to it. It is just the author could have done better and I am hoping that they can make more explainations and solve many people's confusions (go to www.bluetooth.com forum and www.egroups.com bluetooth discussion, it is not difficult to find the common confusions that peopel have) instead of rewriting the spec with better english.