I have headers only, it gave me a bit more torque, but a nicer sound ! for the price, I said why not !
The install is not hard... unless you break a bolt ! Fortunately I did not, but I still took me 8hours on ramps.
I think I wrote something about the install here.... EDIT:
http://986forum.com/forums/diy-project-guides/55540-how-ebay-headers.html