I believe that for product developers who are enthusiastic about hardware, unless you're planning to do a deep dive into the China ecosystem, complete with building professional relationships, opening up a manufacturing services shop there etc., your best strategy for engaging with China's manufacturing prowess is 1) through the community-driven hardware-sourcing sites (e.g. Adafruit here is the US answer to Freetronics) + DigiKey for prototyping purposes, then 2) when you're ready for manufacturing (because you've verified your market!), engage with one of the hardware incubators that have arisen in recent years, whether stateside or in Shenzhen itself.
As accessible as the supply chain in HuaQiangBei is (see TFA), there's a lot of opaqueness when it comes to quality. I challenge you to do a six-sigma caliber audit (think component variation, and the supplier traceability that comes with that) based on the HuaQiang Bei ecosystem that meets the requirements of your customer who in their home country is likely located behind the curtain of a strong regulatory body that needs satisfying. The simple truth of the matter is that these vendors consider revealing their supplier sources antithetical to their way of doing business, and will talk around such queries ad nauseam instead of telling you outright.
Many of those aforementioned hardware incubators are there because they already have long standing relationships with credible factories, so they can reach through the morass of suppliers to those they have a demonstrated work history with.
Some miscellaneous tips: If you're visiting because you have a flair for industrial tourism, then have fun and keep your head about you. If you're planning to be there long term, make sure to reference the experience of expats (say, posted online at least if you don't know such folks) who've lived there long term there to understand non-work aspects to life there which are also important. Build a strong support network of the expats around you there. One undermentioned point is that The Great Firewall will keep you in a communications bubble while you're there, so make sure to get out frequently to stay in touch with f+f and colleagues.
Source: Over a year in Shenzhen.