The Scuba is really a 2-in-1 piece. It's the primary muffler, plus the second catalytic converter of the now-standard 2-Cat exhaust system.
That way, if you have a cat-less header, you still have a cat. Plus, it allows far greater flexibility for the final exhaust to get different sounds without being unbearably loud. The final exhaust piece can either amplify the sound, make it higher or lower, or make it quieter.
With the final exhaust made into a straight-pipe, the result sounds like a "classic" 4-banger (like a 60s British car or the like). With the header then changed, it makes it significantly louder, a bit more raspy (while still pleasant), but with a bit of drone at around 3,000 RPM (less drone just above and below that).
I mention that, as it takes the specific muffler out-of-the-equation. My B has none.
So, the header makes the exhaust system significantly louder and a bit more "raspy" in tone. If the muffler is a bit raspy already (as many are), it will be quite raspy.