I have an X-Force 3 inch on my VY Maloo. I bought it because it was pretty cheap and not many places make the duel system for Maloo (it exits on both sides at the back where as previous versions just exited on the passenger side). I'm not that fond of it, if I bought again I would definitely go Di Filippo. I have a mate with Di Filippo complete system on his ute, the headers give it a really nice crackle and pop where the X-Force is just loud.
Also, if you fit aftermarket headers make sure you get the heat shields for the rubber steering rack boots. X-Force doesn't include these but I believe some other brands do, they are easy to fit when the headers are out of the car.
