The Monty appears to be a good muffler (relative to other available options), and it is also an expensive muffler. It is, however, not a perfect muffler.
The build quality does leave a bit to be desired for a muffler that costs $700-$800. While the body, inlet flanges and tips are all T304 stainless, most of the body is MIG welded rather than TIG welded. Not a performance difference I suppose, but certainly an aesthetic one! MIG welds are ugly and look like they are done by a high school autoshop class just learning the trade. Nice TIG welding is a work of art and is what many, many other muffler manufacturers for other makes employ in their systems.
My Monty had plenty of splatter and extra muffler body material where the inlet flange and muffler body were welded, I had to "modify" (i.e. grind) in order for it to be a nice straight through area free of splatter and material. Mine at least should have been stopped in QC and fixed. Below is a pic before:
I'm also convinced my 2-inlet, 2-outlet Monty must have been assembled on a Friday afternoon after a liquid lunch of Foster's, as my right side tailpipe was 1" longer than the left. Had to cut it down to match the left. How does that happen?
The Monty inlet flanges were also too short to work with George Narbel's headers/adaptor units and the muffler body was hitting the engine mount carrier when I tried to install it. My prior Dansk fit perfectly and visually had longer inlet flanges. I had to get some new 2" tubing and flanges, and than my colleague TIG welded them together at the correct length so the Monty fit properly. Don't know (but I have a guess) whose fault that was: the Monty, George's headers or my car.
Here is a pic of the muffler installed on a Carrera (which won't look too different on an SC):
The Monty muffler is slightly louder (i.e. deeper) on my application than the Dansk. The Dansk did not drone at all inside the car at any rpm and load, the Monty drones a little at lower rpms with some load on the motor. It is, however, not objectionable in my opinion. I have driven/sat in many other 911's with aftermarket exhausts that were completely unbearable for any period of time. I wouldn't hesitate to drive this car on a long road trip.
Ralph