I'd be hesitant to have Medicare Advantage in the U.S. I felt the same way about HMO's when I was a member--okay for minor medical issues but terrible if something major happens.
Recently, Vanderbilt Hospital's refused to accept Medicare Advantage and it's wreaked havoc on their hospital and all the doctors' practices they've purchased throughout the region--1700 physicians and nurse practitioners.
I'm just on Medicare with a United Healthcare supplement and Part D (medicines) bought on the open market. I am covered outside the U.S.
Those with Medicare Advantage should consider taking out trip insurance slanted toward healthcare when traveling outside the U.S., including Canada and Mexico.