dyno-max mufflers good / bad?

On a 440 running through Factory HPs with 2.5 inch all the way back and H pipe
Been on since early 90's
I think they sound great and very little drone even on highway
Click play to see vid
[ame]http://vid1337.photobucket.com/albums/o667/74DartSwinger360/Dads%2068%20Charger%20RT/ChargerWalkaround_zpse9203847.mp4[/ame]