If you want ambiance, you've found the spot. Once you walk in, you'll forget you're in Vegas, and you won't remember until you leave.
It's a pretty random location for such a niche place. Maybe that's what makes it extra cool & surprising.
I got the feeling that there is a normal crowd that makes up most of their business. Lots of creative types, hipsters, people into throwback periods like the 40's and 50's.
Cons- No food. I'm also not sure if they have drink specials or happy hour. Check first.