extras-devel is not a package but a repository for a whole bunch of packages that are pretty much bleeding edge (brand spanking new without any testing done beforehand).

It is probably not a good idea to have it enabled if you're not familiar with maemo environment and particularly linux (including working with CLI as well).

Though many programs that have not been promoted to extras may remain either in extras-testing (where they will be tested) or forever in extras-devel (probably because they were not meant to be for the end users or their usefulness was limited to a few people).