Unless it is a qualification to be an online teacher, it is always better to have face to face observed teaching practice as part of your course. This is not possible with a 100% online course, therefore it cannot be as good as, for example, the CELTA- end of story. Whether an online course could offer better value for money , be more convenient or even be the only available option for some people are the only debatable points.
You cannot work legally without a degree in Thailand.
I did the CELTA and have been a teacher trainer but have not had any connection to any TEFL certificate providers for the last 4 years. If anyone else posting has a closer connection to a particular course provider, I think they should make that clear publicly in every post they make on this topic.