good luck ...both work good for retirees, the O one to me is just a bit cheaper (particularly as you get older and insurance spirals!) And easier once you get past the money seasoning bit and a trip for the extension at 3 months.
for info Stuart, I had a non oa retirement and extensions for many years until I lost it getting stuck in the uk at extension renewal time. After much deliberation (and of course already having the 800k sitting in a thai bank) ...I decided to go for a 3 month non O and then extend within thailand for retirement. Proved a good choice ...easier and cheaper to get the visa in the first place, and extension times prove also cheaper without the mandatory insurance (of course you should choose some insurance, but you now have a much wider choice!)
Just my experience of trying both OA and O retirements
I have my 800k in Krungthai savings account that currently pays I think 0.25% (it varies year on year)....several standard savings accounts do I think ....one or twice a year I do a small withdrawal or top up to ensure the account remains active