I don't have first hand experience with OBX headers for the 3.4 but I do have experience with OBX products. I had one of their catback systems on both of my civics. I bought the first one because it was cheap, and then when I got my next civic I had to have the same exhaust. It fit good, looked good, and sounded AMAZING. I was constantly getting compliments on it and people asking what kind it was. I have nothing but good things to say about that exhaust, but that doesn't mean they get everything right. I know that their turbo manifolds have been known to have some issues.
That being said, are you forced induction? If not, don't waste your time. They are a pain to install, the gains will be minimal, and there a bunch of better things to spend $300 on.