In general Thailand is a dangerous place to work. There is no rule of law, no enforceable contact no guarantees of anything like getting your salary.
The fact that so many reviews are impressed with the fact they got paid is a warning by itself.
This company is not and exception to this rule. The advantage teacher lasts 3 months, up to 50% turnover a semester and over 100% a year.
That happens for a reason. There is no teaching in Thailand. Students cannot fail a class, cannot be considered cheating, do not have to do homework.
There is only one measure of your performance, that is are people entertained by you.
For this reason they are no trained professional teachers in Thailand because teaching is not allowed.
Being paid once a month means people are waiting for their $800 then disappear the next day. Companies will expect you to do this.