For the past few years, a flood of hardware startups based in Silicon Valley have been traveling to Shenzhen to find easier, better and less-costly ways to make products. Following six of those startups on a recent Shenzhen factory tour yielded some interesting trends and lessons, as WSJ's Li Yuan writes in her "China Circuit" column:

1. More factories want startup business. With China’s economic slowdown and export slump, many factories that used to rely on big volume and low margin orders—and were reluctant to take smaller orders—are operating under capacity. “They want business from startups more than...