I would go for a brand new one with the AD...
For that price, can get a brand new one at grey but if you can afford usd5400?
What's 15% extra?
You get a peace of mind, brand new watch, warranty with your name and get to build rapport with the AD...
And if there's anything wrong, you can always go back to where you bought it.
Although there are some good deals to be had buying online or pre-owned... but there are risks as well...