For free you can't go wrong. I've had about 2-4 of those guides and I still have the Disgaea dual guide that pennied about a month or two ago at GS.
I also had Disgaea 2's guide and the Castlevania one and lately I could've got my hands on a copy of Phantom Brave's guide, but I passed since the corners were all bent up on it.
Actually, I just looked at the guide I have and it covers Disgaea DS, the original Disgaea and some version for PSP as well. So it's a triple guide.
But for nothing, you got a steal.