To show a meta box on a page with the ‘default’ template selected (or no template selected) you currently have to do this:
'page-template' => array( '', 'default’ )
Would be nice if the plugin would handle this.
On a side note, it would be better to check for the current page template by using get_page_template_slug( $post_id ) in stead if get_post_meta( $post_id, '_wp_page_template', true ). The former always returns an empty string if the ‘default’ template or no template is chosen.
Kind of related: #305