My dad once said to me, "You give a lot of books three stars." I do.
I think this one is better than the Demigod Files, but I'm still not that into these filler books. If you love Percy Jackson and the Heroes of Olympus it's worth checking them out if only because you get a little more of the characters you like.
I skipped the last story completely though. I don't really care what Rick Riordan's son has to add to this universe. Sorry.