FWIW, my long time Muffler shop doesn't carry Dynomax anymore.
According to them, they had too many "Waranteed" returns over the past two - three years due to faulty build workmanship on the cans...
They tell me that they have never had a "Warranty " return with Flowmasters.
BTW, this is a reputable, "Old Style" Father & Son shop in the Huntington Beach, Calif. area that does a lot of Hot Rod / Muscle Car exhaust system work.
YMMV
PS, My present cars have Magnaflow( it replaced a worn-out Dynomax) and Flowmaster cans....
1991 Jeep Cherokee 4X4- Magnaflow
1992 Camaro RS Convertible (had Dynomax, now Magnaflow)
1968 Dart Gt - Flowmaster