I was nervous making a major purchase, but it appears to be working out.
I helped an Argentinan friend buy a plane ticket. I used a US issued Capital One Master Card. The reservation was in ARS pesos, and I am in BA so bought it online from Argentina, first posting to my account at approx $3400 USD and 5 days later a credit of $1500. That is not a great exchange rate, but at least we were able to get the flight.
I was concerned that a purchase on a foreign airline in ARS pesos wold not be adjusted to the MEP rate. I called Capital One and Mastercard over the weekend, wasting hours, and none of the agents had any idea what I was talking about.
Ultimately good, since buying plane tickets with a CC makes a big difference. It was stressful, I should have made my first purchase a coffee.