I have the Fabspeed HFC with x-pipe mated to a UUC Corsa axle-back and I love it. It sounds fantastic. I have the O2 extenders, and I have never thrown a CEL. I easily pass inspection in Texas. I went this route so I wouldn't have to refit the OEM cats each year to pass inspection.
I agree that fitament can be an issue - you need to hammer out the heat shield around the cats. This video does clearly explains proper installation:
. I've never had a problem with the cats dragging, but the driver's-side cat does hang low.