One thing to watch out for, its got me already twice.
If putting in a Techron or other injection cleaner, or an octane boost; use the funnel. While the bottle looks like it is opening the flap, it is not and all the stuff pours out from under the car's rear fender all over the ground. If that happens or even gas spills take it to a spray wash and spray under that side of the car to get the solvents off.
Last Fall, I had a pump not shut off while filling up and it was not noticed until the gas was pouring out on the ground from the overfill vents in that flap. So now I always watch if very carefully filling up.