I did the OA in England and had to go to Embassy but very easy to do but you get to Thailand you need to open a bank account and put 800,000 in you can’t do 65k a month as you need to have 12 months deposits to qualify. I believe
it’s not unlimited unless you have a long term visa. It’s up to the individual immigration officer. My friend was doing it every three months from Australia and got stopped and told he needed a long term visa and marked his passport so he is now on a non-O