I agree with Flatliner, it's open sourced hardware just like arduino. When you buy from china though, you have to pay close attention to the hardware components used, they're usually lower quality, and some of the ICs are counterfeit which may not have full compatibility or have reduced life.
Specifically with RF stuff, the Chinese designs may be missing RF filters that keep the input or output signal clean
Specifically with RF stuff, the Chinese designs may be missing RF filters that keep the input or output signal clean