I have both versions of the miltek ie a3 and s3. Although the a3 exhaust i have is on a golf.
Different is chalk and cheese. On the golf, 18t, turbo back, its boomy at cruising speeds, so much so miltek themselves ahve replaced it twice in 4 years! Its better, (they modded the rear box due to the numerous complaints) but its still annoying on cruise.
The S3 on the other hand was seriously quiet in the same situations with the resonated centre box, (golf has resonated box too). So much so, I actually had the none resonated centre pipe relaced with a straight thrrough. Again, on cruise its quiet, not at all intrusive, but has a lovely rasp when you open it up!
It clearly is to do with the shape and size of the rear box. But on the quattro models, (TTs too) they work very nicely.
I hear the jetex is very nice on the golf, a better option than the miltek by most accounts.