Even if you hammer in the heat shield they still hang a tad low and will rub on bad speed bumps and such. I loved the way they sound. The only advantage of going with a Fabspeed setup is with the 02 extenders you can probably get by without a tune. I would prefer to have the cats in the secondary position as I feel there is less turbulence after the header that way. If you want to get a tune down the line I would pass on the Fabspeed and go with a testpipe setup or go with the cats in the secondary position.
Just my .02
2013 M3 Coupe-MR/BLK ZCP, ACM test pipes, BPM Stg2 dev. tune and Megan catback, AFE Stg2. with C/F elbow VMRV810 19x10&19X11 275/295 Mich PSS.
Previous rides: 2011 M3 Coupe-MR/Blk
2007 Porsche 997C2S Speed Yellow/Blk sport seats
2004 BMW M3 Imola/Blk