I improved your plugin

I added him some options:
– The use of a CSS or not to display a button instead of plain text (an image button is default)
– The choice of two colors to customize the CSS button
– Whether or not to display this button directly to the end of articles and pages with add_filter (‘the_content’)
– Use EasyFancy plugin for responsive popup

A good idea?

Check here : http://www.restezconnectes.fr/un-plugin-wordpress-pour-recommander-une-page-un-article/