Get 20 or 25% off the base fare (not on taxes and YQ) when using a Visa card to book. Origin and destination will determine if it's 20 or 25% off.
Details, codes to use (they depend on the route) and T&Cs
here.
I flew their J product (they don't have F) JFK-PTY-HAV-PTY-JFK and it's pretty much identical to domestic UA F.