The Essential Guide to Electronics in Shenzhen (2016) [pdf]
Actual hardware R&D focused business owner in the PRD here. 18 years China. IMHO the 'essential guide' is just buy stuff online: barely anyone actually physically visits stores anymore. Certain parties make money and cred by claiming being in physical proximity to a bunch of cables and parts in HQB is somehow awesome, and in a minority of cases walking around might save half a day, but really you can just order ahead or use your own stock if you have a clue which area you'll be working in, and you'll have saved 10x half a day in rent by not being there. Even if you buy stuff online many stores will give you their business card, WeChat or QQ account and you can just ask them to send stuff pronto on subsequent orders, cutting Taobao or whatever online platform out of the equation. Shenzhen is very expensive for real estate and salaries. If you want to go scrappy, live somewhere cheap in China (Yunnan is awesome) and use Taobao. If you want to go scrappy and fast, live somewhere cheap in the PRD and use Taobao. (There are minor electronics ecosystems around Xi'an, Chengdu, Zhejiang and Beijing, too.) No need to even visit Shenzhen, although outer Shenzhen / Dongguan is still a great place to acquire lots of types of industrial equipment, IMHO inner Shenzhen / HQB really just isn't anymore. Hardware startups should go somewhere cheap to iterate. The cheapest and cleanest well connected major area of the PRD is Zhuhai, where we moved from Shenzhen 1.5 years ago. I go back about once a month for outlying factories.