The big unknown are the tax implication? The article should clarify what it means, at least vis a vis Korean tax agency.
Sometimes it’s phrased that any income from your home country while you’re in your guest country is only taxable in your home country. Other times it’s just credited against your local taxes (which could cover everything with a lot of paperwork, or could still leave you with an amount owing to cover the gap).
Sometimes even locally earned income is tax free, but that’s usually only for students.