I really like the book - of course, I do have a garden-related girl-crush on Miss Fowler ;)
If you are looking for a comprehensive field guide this is probably not your best bet. However, it is perfect for an urban environment as it particularly looks at plants commonly found in parks, abandoned city lots and alike. On top of plant descriptions the book offers basic instructions to processing ones bounty such as jam making. I found the case studies about edible landscapes to be interesting, too. Love the look, the photos are very pretty.