I'd likely go this route over a 3rd party remap, I drove a 540i with the power kit and it was noticeably quicker than the stock one. I'd not be surprised if they are putting out more than the power gains they quote. Interestingly they change the torque converter on the 5 series.
I'm surprised it actually felt that much different (if the power figure is accurate). I'm more interested in the noise from the M Performance exhaust than I am the power increase if I'm honest.