I think this is pointless. You are buying a book to learn more about him when the book is about something he isn't even labeled with.

Say this book says 'people with Aspergers do X and Y wrong'. Then he does X wrong. What does it matter?
Let's be honest. You aren't here to learn about the best way to be swept away by Asperger's traits. You are here for the potential negative issues. Are you really able to lower your standards for him because he might have Asperger's? Because that's about all you can achieve, imo.

If you want to learn more about him .Talk to him or do things together. Ask him how he feels.