I feel they are thinking of emissions primarily, but don't realize they can fail with the catted DPs....and yes, the main cats are huge restrictions.
You (Jeff) know this, but (for others) if you leave the secondary cats in place the rasp really isn't present and the smell is minimal.
2011 Mineral White M3 ZCP
Paint Correct, Opticoat, Ventureshield, some CF, B&B exhaust, AFE Intake
2014 Mineral White 328d Xdrive Wagon
stock for now