I have both Amex Platinum and MedJet Assist. There is a significant difference between the two.
If you read the Amex benefits carefully you will see that, like many medical insurance carriers, they have the right to review the medical situation a decide if you can be satisfactorily treated at a medical facility closer to your current location as opposed to your home location. MedJet only requires that you are hospitalized and they will send a air ambulance, assuring that you not only are transported to the hospital of your choice, but that a bed is waiting for you upon arrival. There is no discretionary aspect to their service.
As usual, Ngaire has recommended the best alternative among the medical insurers.