It's a terrible idea. No company would ever sell you something that wasn't better for them than it is for you. when I sold cars we loved it when people bought them. We made a fortune on them. The are hardly ever used.
That's exactly it. If something is going to break because of defect, it will more than likely break before the basic warranty is up. Otherwise the car should be good until after an extended warranty would expire before the big dollar items start to fail. Ford pays actuaries a lot of money to figure out the statistical probabilities of these things happening and where the profit point is at - they wouldn't be offering extended warranties if they were losing money on them.
I've bought two extended warranties, one of them being a Mustang. I didn't need either one. I didn't buy one on this car.