It doesn't matter how long that thing would keep a growler cold and carbonated. The beer has already been exposed to oxygen when the growler was filled at the tap, so if not consumed within hours, the beer will be quite heavily oxidized, stale and unappealing. Growlers are not intended to keep or deliver beer in good condition. They are there to get you home from the taproom before you drink a half gallon of beer, so you don't die or get arrested. So the machine could work perfectly, but that's a red herring; the product it is designed around is unstable. Would be a waste of money.
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