I like this plugin a lot. My client had some duplicate Pages and I run this plugin to search for duplicate titles. But I was surprised that it didn't find any duplicates when it was obvious duplicates existed. It turned out that some titles had "html entities" while other had the real characters, for example: " vs ".
It seems to me that it might be useful to add a call to html_entity_decode on lines 143 and 144:
$post_compare = html_entity_decode( $post_compare );
$post2_compare = html_entity_decode( $post2_compare );