It is true that there is no transportation in SGN but in SGN you have many, many more choices regarding accomodation and not to mention that everything is cheaper in SGN. Also, try to find a taxi in HAN at 4am or after midnight. Almost impossible.
And regarding salary in Vietjet, it s not true. You have to fly at least around 90 hours to get same salary as in VNA and don't forget that you receive only base pay when you are off duty for two weeks. Also, you have to pay for your ticket back home.