That's exactly what I did (sans the video part) in the screenshots above. I dug a little deeper after your post though, and while there are no explicit denys present on the module in question ("Homepage Slider Items", although this happens for EVERY custom module), I did notice that the test_editor user, while it is definitely in the Editors role, doesn't seem to inherit the permissions of the editors role.
I've attached screenshots below.
editors_role.png shows that test_editor user is in the Editor's role.
permissions_for_editors.png shows that the editors role has permissions for the module. This is /Sitefinity/Administration/Permissions>by Role or User>Roles>Editors
permissions_for_test_editor.png shows that the test_editor user does NOT have permissions for the module. /Sitefinity/Administration/Permissions>by Role or User>Users>test_editor
PS - while we're at it - it would be great if we could give the Editors role blanket CRUD rights to items within custom modules so that I don't have to assign those line items individually.