I believe that I also note that it is intended for advanced mechanics and that it might not be the best thing for beginning developers.
As for the .exe closing instantly, you must have an antivirus blocking it or something, and the folder contents are standard UE4 packaged contents…
I feel that you may not be ready to try it and there are better starter plugins out there for you.
Regardless, no its not paid, yes it is for free in all of its forms, it is MIT licensed which grants the user the rights to do just about anything they want as long as they credit the use of it.