Slug metadata not working?

Is the Slug metadata field new? I know I've wanted it for a long time and only just now noticed it on the Metadata page.

Either way, it is not working as advertised.

When I tested it on an old post where I had used the Link field to customize its slug, it just dropped the rest of the Link Format I had defined.

Instead of domain.name/path/to/post/slug it loaded as domain.name/slug

So it basically functioned the same as the Link field.