I'm finding this thread very interesting and informative.
My wife and I are intending to "retire" in Thailand using the non-immigrant O-A visa. We're US citizens, 50+ years of age and will not have any health insurance so the requirement for health insurance hasn't been a reason to go for the O rather than O-A. The perceived difficulties in opening the required bank account in Thailand in a short period has really discouraged me from even considering the O. I would be too stressed.
Upon expiration of either the O or O-A, how does the extension process differ? After the initial two-year (one year + leaving the country and returning just before the initial year expires) I would probably then go for the O as I would have plenty of time by then to figure out how to open a Thai bank account. Even then, I would still have to (or want to) purchase health insurance.
I put "retire" in quotes, because we plan to eventually (5+ years later) return to the USA some time after becoming eligible for Medicare coverage.
Mentioned upthread is that obtaining a health certificate can be difficult in the USA. I'm interested in first-hand experiences.