Just don't take control of Astarion to read the book. If you do that, you have to pass skill checks. Just give it to him after unlocking it. He will read it on his own without having to pass skill checks. Make sure Gale is not in the party when you unlock the book though, or you might not even get the option to give it to Astarion. Gale apparently takes precedence.... madness
I still wish it granted us something more interesting though... interesting and evil.
