How strong is the manufacturing industry in Shenzhen?

Not just Shenzhen, but the industrial chain of Shenzhen and the whole Pearl River Delta region around Shenzhen, including Huizhou, Dongguan and even Foshan Zhongshan.

Maybe a company in Shenzhen will produce a design and send it to Huizhou factory. The factory can find all parts suppliers in one day, and the products can be mass-produced in one week. Moreover, the land transportation is developed and there is no logistics trouble at all.