FeedSignature puts a link back to your original article in RSS feed to get a backlink in case somebody copies it from Feed. If the copier is simply using an automated tool to copy your RSS feeds, you will get a link back to your article automatically. More links means better Google ranking. So, you are building your links without any extra effort. The original article text and link is NOT visible on your blog article as it will signal that you have also copied the content. The extension only adds it to your RSS/Atom feeds. It is not sure if Google or any other search engine can identify that a particular blog entry is copied on the basis of this 'original' article footer or not but it certainly helps readers/users find out the original source. May be Google's algorithm is also tracking these kind of text to find copied content.
This BE extension adds an open graph meta tag to your blog post with the first image in your post. Facebook would show this image as a thumbnail on its pages when people share your post.
The extension is pretty simple and uses Google's chart API to generate a QR code for your post's URL. The user can scan it using his mobile's QR code scanner application. Once scanned, the embedded post URL will be read by scanner and user can visit it on his mobile without typing anything. So, it actually helps you share your posts without even using any Facebook, email or any other online sharing mechanism.