My wife and I are both on a United Health Care Plan and have used it while traveling without a problem. When getting a supplementary plan, keep in mind that the coverage for a given plan (we chose the F plan option) is the same no matter what company provides it. So, research and/or get advice on what plan will meet your needs, then get rate quotes from several companies to see who has the best price. AARP United Health Care has very competitive rates, especially in the early years of coverage due to their discount which gradually diminishes. And, they also give a discount for married couple status.
We have not had any problems with insurance claims or billing issues. But if at a given point I discover that I can get the same coverage at a lower price from another reputable insurance company, I wouldn't hesitate to change
AARP may be considered liberal, but if you are concerned about social security and medicare benefits, then you need to appreciate their presence even if you don't agree with all of their viewpoints.
Moderator...if I've gotten too political with this response, please feel free to delete this post. I don't intend my response to be "political".