Originally Posted by
mysterym
Answer is that it is unfortunately not compatible with free day coupons.
That is overly broad.
If you use a third-weekend-day free coupon on a rental, and pay for the first two days, Amex should cover you. But if all days of your rental are paid with free-day coupons, then I would expect you to be out of luck. And if you use rental-car-company "points" rather than coupons, it sounds like you'd be out of luck too, unless the points somehow get converted to a coupon first.