I got the Familiar Folio in print, and it has a lot of information. Like for instance, there is familiars based on your Arcane school. This information is good for wizards that specialized in some sort of arcane school (I'd include Sin Mages as well). And there are other familiar types and archetypes for characters without a familiar normally.
Of course there are new spells that work with your familiar. New improved familiars, tiny familiars, small familiars, new equipment and magic items, and other options. If you play a wizard, sorcerer, or other class with a familiar this book is something you should pick up. It's worth it.
I enjoyed this book (I got the print edition). It offers good options for use for a player with a dragon bloodline. And I don't mean just the sorcerer bloodlines, although they are in there too. There are options and archetypes for your use. Well worth the price.