Average 'fringe' in China, defined as social insurance paid to government, state pension, etc, averages 40% of salary for most employers like factories and BPOs. Total cost of employment per employee in China is more expensive than most of Asia.
Overtime of more than 36 hours per month for each employee is illegal in China, and the court always sides with the employee even on the scrappiest amount of evidence.
China makes up for this with awesome infrastructure reducing logistics costs a lot. Wage costs are only around 15% of total cost of production for a factory like Foxconn.
Some factories do not provide great conditions, but these are mainly small factories with no gloves when handling pollutants, etc. When I mention small factories, I mean a warehouse with wooden tables, anything with plant and scale is monitored closely. Monitored by the public with mobile phone cameras as much as by officials. There is a strong public backlash movement on the Chinese language internet and it is effective.
On glass vs. plastic... China can be incredibly agile especially when dealing with partners that are privately owned properly licensed companies which lack global levels of bureaucracy. Today, in my global multinational, I was requested for 3 directors' 'approvals' for the acquisition of 3 new IP phone sets, while another request which goes through another route which, for 50 desktop units and 100 screens, did not require any 'approval'. Do not discount baggage slowing things down.