Well, this is anecdata, but when I was an atheist, I found God Delusion frustrating and not worth handing to my Christian friends, since it attacked lowest common denominator Christianity a lot, and my friends tended to be nerdy Thomists. Plus, I find a lot of Four Horseman stuff frustrating because they rarely construct something of their own to defend (though I understand the sense of urgency to knock people out of their current worldview -- if you find it abhorrent enough -- and let them land where they may).