I think as long as FetchContent works it's super easy to try out your library and see if its something that should be pulled in as a real dependency.

I have heard that FetchContent can make something unreliable, as in dependent on having a connection, but I think it opens up the door for a lot of people to be willing to try it :) (That, and you can turn off mandatory updates, making it work offline too).

I think the basic rule for making FetchContent work is to just put the CMakeLists.txt in the root directory and then make sure that you can use the project as a CMake sub-project.