If you are concerned about third parties manufacturing your device and/or using your device in China, then you need to protect your invention by means of a Chinese utility model and/or a Chinese patent. Both the utility model and the patent may protect the invention so that you can forbid others in China from manufacturing, selling and using devices falling within the scope of your utility model and/or patent.
The differences between the utility model and the patent are:
- The protection of the utility model expires sooner: the lifespan is 10 years vs. the 20 years of the patent.
- The utility model is published way sooner than the patent: it takes few weeks or months to get published vs. the 18 months it takes the patent to get published (unless you request early publication, which I am not sure it is possible in China).
- A Chinese utility model is way cheaper than a Chinese patent.
If you publish your invention somewhere, should a third party apply for a Chinese patent or utility model there is a risk that the CNIPO (Chinese Patent Office) will not find your disclosure and, thus, the patent may be granted. A Chinese patent or utility model would not allow you to import into China, manufacture, use and/or sell your device in China. Currently, the Chinese patent law regards a public prior use occurring anywhere in the world as prior art, therefore if you build the device and publicly use it or you give it to somebody, that would be prior art; obviously, it is unlikely that the Chinese Patent Office gets wind of it, so a Chinese patent could be granted to the third party anyway (in the event that no other prior art affects the novelty/inventiveness of the invention), but in theory you could get such patent revoked if you are able to prove that you disclosed the device at a certain date.
There is no grace period in China, therefore if you disclose your invention before applying for a patent or utility model, your own disclosure would take away the novelty of your invention, thus you would not get the patent granted if the CNIPO finds your disclosure (which is quite likely since the first search the examiners carry out is disclosures from the inventor/applicant). Some (and not that many) countries have grace periods if some requirements are met, so a disclosure by the inventor may not prevent her/him from getting a patent granted filed later on (up to a certain date from the original disclosure).
Having a Chinese utility model could be a good idea because it gets published soon in Chinese language. Even though the Chinese examiners do not limit the prior art searches to any geographical location, they tend to cite Chinese documents during the prosecution of Chinese patent applications because when they filter using keywords they do that in Chinese rather than in English, then the likelihood of stumbling upon a Chinese document rather than an English document (say a US patent application) is greater because the machine translation of the keywords into other languages is not that "perfect". It could occur that you have a published document in English and a Chinese patent is granted to a third party, you would have to initiate a reexamination/nullity process in China to get that patent revoked, which is costly.
In China you are allowed to request both a utility model and a patent, and unless this has changed recently (I do not think so but I am not sure), you should do so by filing both on the same date, either as a direct national filing, or claiming priority from a previous patent application via Paris Convention (not through PCT route). If you do not file them on the same date, the application filed later will not be novel over the earlier filed one, even if you claim priority from said earlier application.
To keep costs to a minimum, you would have to directly contact a Chinese IP law firm that can assist you in the filing and prosecution of the patent application and/or utility model rather than doing it through an IP law firm from another country since quite probably that would increase the overall cost (it would depend on the rates of the Chinese patent attorneys hired by you and by the IP law firm from another country).
Bear in mind that patent protection is a matter of national law, therefore in countries in which there is no national patent granted in principle the device may be used and produced.