If you send any sort of marketable product to China, expect that it can and will be duplicated and sold in competition with you.
China sells tons of products they cloned from something pre-existing. I know because I own some of it and I've seen lots of western companies making use of it too. Here are a couple of examples of products from Amazon that existed long before China started producing clones.
https://www.amazon.com/BIG-RED-TAM82012-Hydraulic-Carrying/d...
https://www.amazon.com/BILT-HARD-Vertical-4-Stroke-Compliant...
All that being said, my best advice is to refine your design locally first, before farming out mass prooduction. Lots of local machine shops can fabricate simple custom metal parts --- they exist just for this purpose.