There wasn't a great deal of noticeable difference, performance wise, after changing the exhaust system.
It certainly seems to pull better in the mid range and the low throttle rideability is unaffected.
No, I haven't had an ecu flash but have had it on the rolling road at my dealers and there was a slight gain in torque and bhp, nothing to get too excited about, but more importantly the fuelling was fine across the range.
I did have to fit a 'Pairs valve' blocking kit as the popping and banging on the overrun was terrible, far to loud for me to live with.
Noise wise, this K-Factory CRS system when fitted with the supplied baffle (DB killer) is definitely louder than standard but not so antisocial that it attracts unwanted attention. I did have a full 'leo Vince' system fitted before this one and that was a lot louder, to loud for me, hence the change.