I got a Blueflame Turbo back on my MK3 Cupra and it dead chuffed with it. Not stupidly loud but gives a nice roar when on boost and is quiet enough when pottering around town. Really to see any noticable perforance gains you'll need to get the turbo back with either a decat or sports cat.
I few of the mk3 boys complain that the miltek knocks abit, but its still a quality exhaust. Id go for Blueflame though, priced better than the Miltek aswell