In American English "next best thing" means second best. It is used to suggest an alternative when you can't get what you want. "Don't have Coke, maybe get a Pepsi, it's the next best thing."
"Next big thing" means upcoming good thing.
I've seen it used both ways, "next best thing" is one of those phrases at least in American English that is highly context-dependent.
Which still makes it a bad choice for marketing copy.
They want something that isn't likely to be misinterpreted, and I've never seen that phrase used to mean "next big thing", only "second best".
As an American, I can't recall "The next best thing" ever meaning "second best' but rather the up and coming latest and greatest thing.
Big country though, could be a regional thing.