My 2 cents...
Shenzhen Air actually paid the full taxes due. Or at least I got stamped "chopped" tax receipts and a copy of the Chinese tax return which is all I really cared about. It worked well and I accumulated a tax paid surplus.
Also, I was there on a non-commuting contract and can concur that the ATC system and general frustrations of Chinese airlines can wear a person down rather quickly. Having said that if I went back it would be on a commuting contract. Just knowing I was getting out of mainland China would be all the motivation I would need to make it through a four or six week rotation.