do you normally rely on patterns when making your quilts? if yes, then read the descriptions posted by the online sources. if the book teaches a technique you believe will be helpful to you, AND if the book includes several patterns and layout suggestions then it's worth the price.
consider the average price of a pattern ... about $7. divide the price of the book by the number of patterns in the book. if you use patterns a lot in your quilting, the book will very likely save you money over the longrun.