$this->get_gizmos wasn't needed when saving the post_meta. Without doing this you wouldn't be able to delete the last remaining gizmo.

$this->get_gizmos() would return all of the gizmos if the $key provided wasn't set in the gizmo array. This would return an improper result.

If $gizmo_data is false or not set then abort the render function to prevent a PHP notice from showing.