I have the Megan Exhaust on my E92 M3 and I found the quality to be excellent. The welds look beautiful and as far as the clamps are concerned I don't see any leak happening as they mated up perfectly. As far as drone, maybe a touch around the 2400rpm level, but it was minimum. A lot less than what I expected.
My car currently has the Turner Test Pipes on the car with the remainder of the stock xpipe. The car is quite aggressive but it could be a tad more if I had my way. I am just so used to my 997S with AWE 200cpi cats and Borlas along with X51 headers. My 997S was insanely loud...
As far as any hp loss I highly doubt it..the bends are smooth and they are really just 2 straight through mufflers mated together.
A great deal for $500 (what I paid).
2013 M3 Coupe-MR/BLK ZCP, ACM test pipes, BPM Stg2 dev. tune and Megan catback, more to come
Previous rides: 2011 M3 Coupe-MR/Blk
2007 Porsche 997C2S Speed Yellow/Blk sport seats
2004 BMW M3 Imola/Blk