It seems to get a little louder over time. I've used it twice. Took 5 years (with no snow/ice/salt) to rot a muffler out, Flowmaster kit took about as long, too.
Dynomax fits almost perfect, but you may need to trim a little of the right rear pipe section to keep the mufflers/tips from contacting the body. Easy fix with a sawzall and good blade. Had to do that both times.
97 LX, 4.6, Dynomax catback, Mustang MAF/intake tube and Aviator throttle body, Xcalibrator2 by Lonnie at BOC, 180 t-stat, Super Coupe wheels with 235/60/16's, Kenny Brown strut tower brace, Tokico Blues, Eibach Pro-kit, some strategically placed MN12 Performance polyurethane pieces, '02 Grand Marquis transmission
Submariners do it deeper...