If they're meant to be a one-time purchase though, I do feel that it would be more appropriate to have one for each PC, or perhaps a single book that applies the benefit to both when read.
Why? An RPG is about though choices. It's up to you to decide whom of your chars should benefit from reading the book. The same mechanisms were already present in the old Infinity engine games for a reason. These books are not about stats spamming. Actually I think the teller of secrets should sell these books at all. You should be able to find them in the world though but they should be extremely rare.
If you find an unique item you only get it once. Only one character can use it. That's how the system works. Tough choices and trade-offs.
@dlux
May people have reported that. Either the glitch isn't fixed at all yet or it only works with a new game atm.
