As stated above: Yes, on the stock JCW exhaust, both are always open AFTER passing through the muffler. There's only one downpipe and one exhaust pipe to the back of the car. That one pipe goes into the muffler. Two exhaust tips then come out of the muffler (for looks) out the back of the car. The pro exhaust splits that 1 stock exhaust pipe into 2 sides before the muffler. Then one side goes into the muffler and the other side STRAIGHT out the back of the car. So by opening the flap, the exhaust goes AROUND the muffler....from the down pipe straight out the back of the car, bypassing the restriction.

Is there a difference? Absolutely with sound. Much better in my opinion. Not so much on performance....by itself. But as with most aftermarket products, it is designed to work with other aftermarket products. Where you will see the difference is when you add / change other components (intake, downpipe,...).