This owner is going to be very happy with their kit. I have had an excellent experience and my car is running healthier than ever. I take great care of my car and prior to installing the SC in December of last year, I made sure a complete check of all engine internals were done prior to installing.
The car runs healthier than ever and the software even helped cure some strange throttle response that I was having with software from a well well established BmW aftermarket software/performance tuner.
The 540 kit is a great addition for this car and by the sound of the OP and the cars he owns, he is doing this merely to enjoy the added driving pleasure of an already well rounded drivers car.
I have known owners who have bought other tuner kits out there that have a great reputation as well, but it does come down to how the car was prior handled or treated in some instances and how it was installed.
Good luck to the owner and enjoy in good and safe fun!!