I installed it and see what you mean. After the user submitted the page for email their is an iframe inserted into that box with this code.
https://pastebin.com/HKAR7Jct
As well as an ad.
https://pastebin.com/vs6KyWGG
On top of the ads that benefit the plugin author the email generated does not point to the post that you emailed about, It contains links like these two.
https://mandrillapp.com/track/click.php?u=30109106&id=e9101d9b977d4e5c806d68113af8c0c9&url=http%3A%2F%2Ftest.blog.dembowski.net%2Fthis-is-a-test-post&url_id=f80a458300a650e2bbb3fd57f0ce3b9d9ccec58b
https://mandrillapp.com/track/click.php?u=30109106&id=e9101d9b977d4e5c806d68113af8c0c9&url=http%3A%2F%2Fwww.printfriendly.com%2Fprint%2F%3Furl%3Dhttp%253A%252F%252Ftest.blog.dembowski.net%252Fthis-is-a-test-post&url_id=6e091cb8cd35aaf0d36991fa85c4641ef79ce90e
I know this is software as a service but that really seems to be a bit much. All this plugin does is provide a popup link for emailing people about a post. That email doesn’t contain much and that tracking and ads are IMHO over the top.