It's the thickness of the welds, the quality of the metal, thickness of the metal, and the longevity of the packing in the muffler.
The sound will change over time because the packing will break down.
The welds may crack.
The tubing will be thin walled, and will be prone to cracking because of heat. It happened on a cheap downpipe I have.
You spent a lot of money on a good car, why skimp out now?