Like a couple of the guys have said, i think it comes down to the centre where its made. The local shop to me (Power & Performance) come highly recommended by a lot of people and they take alot of price in thier work.
I use alot of sportex systems as they are one of my suppliers, fitted one to my gti the other day (car now being sold) sounds gd, not too loud just adds a nicer tone and it fills the cut out in the bumper. i would like it louder as i like a loud exhaust but i cant complain about the system