I've been reading this with interest and will be ordering my N55 midpipe. Thanks for posting your results, guys, progress needs these inputs.
Re: The M button; There are some conflicting reports on here which all appear credible to me, I think the thing we are missing is that all 1Ms round the world are not the same. We have already seen that some markets have two of the tailpipes plugged (China) and, believe me, there are many other differences in production cars to accommodate the different laws and tax regimes that the car manufacturers face.
In the UK we are taxed on CO emissions which is tested in the default mode when the car is turned on i.e. with M (or Sport on other cars) turned off. The manufacturers therefore put an emissions optimised tune into the car and only give us the "full beans" version on the M button.
In other markets this wouldn't be necessary so it is entirely feasible that some markets will show extra power from the M button while others won't.
We also have an R60 Mini Countryman S and it is especially noticeable on that, improved economy with the Sport off and power with it on.
So I think its likely that you're all correct.
Btw, I have been trying to find out if anyone is bringing Maddads into the UK, anyone know?