I haven't heard the Meistershaft yet, but I want to. I believe Mark when he says that it is loud, and I want to hear it so bad. However, back in my E60 M5 days we had an old nickname for the Meistershaft exhaust for the E60 M5, and that was Meisterslow, because they didn't really make any power.
I have the Full RPi GT system on my F10 M5 now, which gives the highest power gains on the F10 that I've ever seen, but it is way too quiet even without secondary cats and no resonators. So I have decided to go the route of having RPi design me a one-off complete muffler deleted section 3 that I hope will be as loud as the Meistershaft system. My new section 3 should be done in about 4 weeks. I don't care about drone, as I used to say, if you've never driven an E60 M5 with a full catback exhaust, no resonators, and straightpiped headers, you have absolutely no idea what drone is! LOL!
So anyways, I hope to hear the Meistershaft before I get my muffler deletes on my F10 so I can compare the two.