AMEX insurance in CR will only cover the damage to the car. They are not able to cover liability insurance in the event you cause property damage or hurt somebody. For that you will have to buy their insurance. You will save some money charging it on AMEX, but the lion’s share of the insurance is the liability. When we rented a year ago, we got a great deal on the car, used AMEX, but the mandatory liability insurance actually cost us more than the car rental. It is expensive, since there is no competition. Call AMEX and they will explain it all to you.