Hi idansh,
The Automatic AMP plugin is a great simple plugin that does the basic job of converting your posts to AMP format. PageFrog is designed to provide all the features surrounding the publishing of AMP pages.
Here are a few things that PageFrog adds to the publishing experience:
– Mobile previews in the post editor, allowing you to see how your page will look in AMP format while you write
– Ad support, allowing you to connect your AdSense account and serve ad units in your AMP content
– Analytics support, allowing you to connect your Google Analytics (and other platforms) account and track traffic on your AMP pages
– The ability to enable/disable specific pages (other plugins are either enable or disable all posts without individual post flexibility)
– Styling options for you to customize the AMP page with your own brand logo, font, and colors
– Bundled with support for Facebook Instant Articles (and Apple News coming soon) so you can manage multiple mobile formats with a single plugin
Long story short, the PageFrog plugin actually uses the Automatic AMP plugin to perform the core basic task of optimizing posts for AMP while PageFrog itself adds all the very important elements listed above.