Our extension guarantees up to 97% rating if the fast server and default Magento theme are used. A lot of things depend on how the server is configured, how the theme is developed, etc.
The module optimizes Magento. But it can not affect the server, the quality of connection and other important params that Google considers.
The Google Page Speed Optimizer extension affects the following metrics:
2. Defer offscreen images - using Lazy Load offscreen and hidden images won't be loaded immediately.
3. Eliminate render-blocking resources - JS files will be moved to the footer
4. Properly size images / Serve images in next-gen formats - the extension uses the 3rd party tools for optimization
5. Keep request counts low and transfer sizes small - using the Advanced JS Bundling feature and JS Minification will significantly reduce the page size in kilobytes and increase the page load speed. Google rank for both mobile and desktop will be improved.
6. Serve images in next-gen formats. The correct functioning of the extension requires some special software to be installed: JPEG optimization tool / PNG optimization tool / GIF optimization tool / WEBp tool.
You can check how your site looks like for Google at PageSpeed Insights and see what metrics can be improved by our extension.