Easy and efficient plug-in. No need to mess with code. Just go to the settings panel and select options. I was so stressed out last week when I tried a similar plug-in that didn't show the thumbnails because each post had to have a featured image, blank thumbnail placeholders also showing on homepage,etc etc.
The beauty of this plug-in is, it takes an inserted image in the post as the thumbnail. It doesn't require a featured image.
Thank you for this plug-in!