Its very difficult to get any type of semi-permanent/permanent work visa for foreigners in China. A lot of foreigners who go to Shenzhen to work on a hardware start-up, are doing it illegally in technical terms. They are all on business visas on which you can't start a business in China. And beyond just work, civil liberties are extremely limited in China. You are good as long as you don't get the government looking at you.