Although the bad reputation of China with patent protecting, In the last few years, the Chinese government invested a lot to help foreigners fight copiers and patent breach. So if you want to protect your investment in China, you should do it the right way, with local lawyer who can protect you investment.
Part of the solution for working with suppliers in China, and keeping your investment, is using a local wording of NDA, being written and signed by a local Chinese lawyer. This way, the factory and/or supplier, will understand he should not breach the agreement, and your knowledge will be protected.
There are other ways to protect your knowledge, even without any agreement, NDA or patent. One of them is choosing the right suppliers, the right building process of the final product, and the way you do quality control. We have a wide experience in this field, and helped client protect their invention, without having the need to invest a lot of money in patents, etc.