Not to be a turd, but it's CACAO nibs, not COCOA. Pronounced like a large artillery gun going off. Ca-COW!!
Back on topic, I've used the cacao nibs in secondary and they were ok, but I would agree with others that it provides more mouthfeel and some aroma, with little flavor contribution. Recently I brewed Jamil's Chocolate Hazelnut Porter, and that recipe called for an 8 oz addition of cocoa powder at flameout. I got a lot more chocolate character from that than I ever have with nibs.