I’m skeptical they actually smoke the meat for 3 days. my understanding is anything past 3-5 hours of smoke is not doing anything for flavor, and you’re better off just steaming or baking at that point. IIRC they do finish with steam even after whatever smoke process they have, which further leads me to believe they aren’t smoking for 3 days.
they also don’t use brisket exactly, it’s a slightly different cut, called belly or plate. something like that. not very easy to get a hold of.