It is 3" inlet, 2 1/2 inch outlet; it is a factory replacement. The benefits are a much smoother transition from the turbo to the cat and it's 400 cell. O.P. is looking for a quiet down pipe option and this is probably going to be the best of both worlds, and, it is very reasonably priced.
Food for thought... My existing MBRP catted downpipe did nothing to my exhaust volume (still on factory catback)
It's a factory replacement too if you're looking at it the same way you view the magnaflow
It's 3" all the way through, it does not bottleneck down
Why Magnaflow markets this as EPA anything is really misleading. Changing the catalytic from factory before 8yrs/80k miles is illegal if anyone cares about that kind of thing. and factory warranties cover a replacement if deemed damaged up to 60-80k miles usually...
At the end of the day, it's my opinion, that a catted downpipe, from ANY manufacturer will not affect sound, all else being equal. Ideally it's a "high flowing," CELL count, but not so high it's not that much better than stock. What Magnaflow advertises, is a catalytic they have certified and tested withe EPA to meet minimum testing criteria. Not for this car, but just the catalytic itself. They then use the same cat on different systems. So IMO, it's probably the 2nd worst flowing system, next to stock over all the other 100-200 count catted systems.
Oh and OP, buy used. No point paying for new, when these kinds of parts will last a long time generally. I think I paid around $250-$300 or so used (coated at that) for mine.