CSON has a few "pros" in comparison to other JSON library for C.
When using CSON users can make the library use their own implementation of a data structure instead of being forced to use the implementation provided by the library itself. This might make the library a bit "convoluted", thus inspiring the name for CSON (Convoluted JSON).
I don't know if there are any others advantages of this library in comparison to others.
CSON uses the GNU GPL Version 3.