Illegal?
 

So I have heard that cat-back exhaust systems are illegal in some if not most areas. Why? Are they louder than most?
Also I know a lot of higher end mufflers like Magnaflow and Borla can claim hp gains but wouldn't there also be a drop in fuel economy? If just seams those two things have that correlation.
Any way I know Magnaflow has one.

http://www.magnaflow.com/02product/s...ll&id=3966

What do you think?