As of 2 years ago the expats in Sanya were doing mostly 1 days trips with maybe 1 overnight a week. The Sanya pilots spent the night in Harbin or Shenyan, and the PEK guys spent a night in either Sanya or Urumqi.
When I was there it was one of the better gigs in China. The company treated the expats well, and the fines were not as frequent as some other airlines in China, notably Hainan Airlines. If you got fined at BCA, you probably did something blatantly wrong that you could have avoided. Fines are part of the regs.
Almost everyone I worked with is now gone for various reasons. If you are a surfer Sanya is a good deal. Also the air is clean. Other than that it is a secondary city in China. Very few expats, or expat friendly services. No western medical care. It is difficult and expensive to commute out of Sanya. You have to fly out to another city in China to connect to an international flight.
I was also wet leased out to Lucky Air for 6 months. Similar flying to BCA. Kunming is OK. Air quality is OK. More expats than Sanya, but not as good as PEK, CAN, or Shanghai.
BCA, Lucky, and Tianjin are all part of Hainan Group and all are just subsets of Hainan Airlines. They share ground staff at each others' bases. Operationally they are the smoothest operation I have ever seen in 25 years of aviation.
And the money is very, very good. At least the months when you are not med down and not getting paid. It is still China.