Don't be too sure about that. I know of a young British girl working on a tourist visa at a local language mill in the town I work at. We will celebrate her 24th birthday next Friday. She has never taught one day in her life, is here illegally, has no educational training of any kind, and works 36 hours a week for 7.5 k a month all while her employer changes her working hours all the time. I work at a public school near her and earn 5.8k a month for working 13 hours a week. I dare to say that she is not better off than I am. Granted she is a very nice girl and maybe a better person than me.
I am certainly glad you are doing well at your present location, but on the whole language mills are abusive and deceitful. I am not taking anyone else's opinions here but from my own observations and experience. From what I have read on this site, the most awful cases of abuse are private schools with a fair mix of public ones, but in lesser numbers. It is a choice between eating an old apple and a bad apple. I prefer to eat old apples than bad ones.

But is she happy, because you didn't actually say? She could be happy enough with her hours always changing-It could be that you are saying she shouldn't be? One can be happy working 36 hours a week and miserable working only thirteen; or the other way around. I gather 'language mill' is a smart-alec dysphemistic dismissive term for an English Training Centre? I assure you I am not calling you a smart-alec, because you sound quite measured and reasonable to me.

Thirteen hours could be ideal for you, as long as you have plenty to do in your free time.

I think you mean you prefer to eat old good apples to old bad ones, owing to the fact that it's the old apples which are usually rotten-I assume you meant to say rotten?

I hope that it's a smashing birthday party.