The smf doesn't wear out like the dmf does, the clutch used is also good for a tune as it has a stronger clamping force. Some people reckon the dmf is smoother but I had the G60 smf on my last tdi car with the AGR engine and think it was definitely smoother. I'm going back to the G60 and sachs kit later on, the clutch and dmf that came with my latest car was fairly new and that's the only reason I'm using it. I've also heard it said that the dmf can help protect the gearbox but haven't read any proof on that yet and don't really believe it as the smf pressure plate has the springs instead of the flywheel.