Hi Bretty, and welcome.
Vietnamese beans are predominantly robusta, and they probably roast them in butter to taste a bit palatable because theyre not as smooth as higher grade arabica.
As for shelf-life because of the butter factor :-/ - good question!
2 weeks is the standard snob belief in life for roasted beans, but admitedly Ive never roasted beans in butter and compared longevity.
My thoughts are that butter has a low burning temp, and so you might have in your stash nice smelling popcorn but not great beans - by nature, and short roasting time.
As for weasel coffee, didnt know Vietnam had Luwaks. Might be hype.
How did you get it through customs BTW? ;D
PS, Gday long-term snobs - havent posted for a while. Good to see some familiar names.