You can go direct to SF, no need for an agency.
There is at least one member on here who works there, but he does not check in very often. He moved from another China job to SF and likes it. I have a very good friend who has been at SF since the beginning and he likes it.
It is night flying, but their schedules are generally around 50 hours/month. They are getting 767s this year so if you can wait to go on the 757/767 that might be a better deal over the long run.
Shenzhen is pretty expensive for housing, especially the Shekou area. So you need to factor that in.
Good luck,
TP