Great pics! Maybe the difference is just the EU/Tuv certification vs no certification for the US PE part. I think on the muffler there is a plate welded on it with the market in which the exhaust conforms to.
I think someone posted that the PE's are made at the MINI factory where the JCW parts are made. Not sure if that is true or not. I would install that rubber bumper part. Exhausts tend to also grow as they warm or get hot. So its quite possible during hard shifts that that rubber part might be needed. ?
Everyone has said that the exhaust takes a few thousand miles to carbon up and change tone. At first most people say its kind of raspy, which changes in to a deeper tone.
The Y-pipe makes for much sweeter noises. More pops and gurgling when cold. But the N55 is kind of louder than a N54 overall. Drive it for while and see what you think. But most people install the y-pipe sooner than later.