@Osian *******
with the non-O you'll need to have money in a Thai bank account to get the 1-year extension. This money is your "security" if anything happens, so Thailand has assurance you can take care of yourself.
With a non-OA you can get almost 2 years in Thailand without ever having to go to immigration or have any money in a Thai bank account. So the required insurance and everything is to replace the large Thai bank deposit to show if anything happens you can take care of yourself without becoming Thailand's problem.