ZZ Fab has one, and Ive actually seen trucks running it. Never seen anybody running the Banks manifold. I saw a pic of one from Wicked Diesel, I believe, but I dont know anything else about it.
If your making some pretty good power, you might see a gain. But for a mildly built truck, your moneys spent better elsewhere IMO. You gotta pull the head and have the factory manifold machined off, as its cast as one piece with the head. Then holes need to be drilled and tapped to mount it up.