Below is the description of extrepo in Trisquel 12 main:
External repositories are additional software package repositories that
are not maintained by Debian. Before extrepo, maintainers of such
repositories would suggest that you download and execute an (unsigned)
shell script as root, or that you download and install their (unsigned)
package, which is not ideal for security.
.
The extrepo package tries to remedy this, by providing a curated list
of external repositories that can be enabled by a simple command,
allowing unsigned scripts to be replaced by a simple "extrepo enable
example.com_repo".
.
Note, however, that while the repositories are curated, and that any
repositories with malicious content will be removed and/or disabled
when detected, no warranty is made by the Debian project as to the
security or quality of the software in these third-party repositories.
I installed it as I just found out about a package that has an external repository supported by extrepo and I also see that one can install packages from non-free and contrib licenses by modifying the config.yaml file. I am not sure if this is the right place to report this.
I think I understand now. I am able to search for it just not enable the non-free software repositories.