Add the opportunity cost of grounding the plane for about a month to apply the coat, plus the cost of the coating. It can easily outweigh the savings or push the ROI to over many years.
LOL 1 month and minimal costs, for years of reduced fuel costs, someone did the calc above and its ~35m in savings a year seems worth it to me given they list the ROI of the film at 2 years.
Yeah but planes fly a lot over the span of 25 years or so; granted, they need to be repainted every once in a while. It does add up, is all I'm saying.