OX is an incredibly rare visa to get. Probably because of the 3m baht stipulation. Prior to all embassies going online you almost only ever seen it from the Sydney consulate as they were the only ones that would sell it with funds in a local bank account.
Since switching to online there are almost no posts about it, which suggests it’s incredibly rare to get
You can certainly use a Non O once a year. It’s up to the embassy that issues it as to whether they’d do it multiple times but no real reason why the shouldn’t.
Visa exempt entries back to back or after an extension will certainly raise red flags.