I work offshore and do 1 month on 1 month off for last 15 years and was using visa exempt stamp for a couple of years then got told that I would get stamped in this time but would need to get a proper non o as it was obvious I was living in Thailand so I got an non o as I'm married to a Thai and now a retirement extension as I'm over 50
If you get a multi entry o visa you can come & go as much as you like . I work overseas 1 month on 1 month off and that's what I have no need to get a reentry permit