I did not use this book as a follow on from Book 1. However, from a quick look at that book I am guessing that it concentrates on the key of C and Am. The so-called home keys of the ukulele.
This book takes the advanced beginner further using a few more useful keys. It does this by introducing the keys and then presenting popular songs that use the chords within that key. The songs chosen are fun and well-known. If you have a good ear, you might even be able to recognise that those chord changes are behind other well-known favourites. So, for example,"Uke-In' the Rags" (P31) provides you with the chords and sequence you would need to play Robert Johnson's "Hot Tamales and they're Red Hot" while track 13 provides the changes behind the blues standard "Make me a Pallet on your Floor".
The book is also very good at explaining and illustrating more advanced strumming techniques. On top of that, there is a great section on boogie-woogie picking.
Overall, I think you will have hours of fun with this book and really feel you're getting somewhere with the instrument when you finish it. What more could you ask from a tutor book?