Link post title to external link - works best for link post format

functions.php

<?php

// Link post title to external link

function afn_link_filter($link, $post) {
     if (has_post_format('link', $post) && get_post_meta($post->ID, 'LinkFormatURL', true)) {
          $link = get_post_meta($post->ID, 'LinkFormatURL', true);
     }
     return $link;
}
add_filter('post_link', 'afn_link_filter', 10, 2);