The one thing to know about Joomla
A visual editor can remove script tags when it sanitises the module. Paste the code in code mode and make sure your user group is allowed to save scripts.
Where reviews belong on a Joomla site
Use a Custom module assigned to the menu items where reviews should appear. Put an inline widget in the main content position, or assign a compact badge to a sidebar position.
Full-width sections suit carousel and grid layouts; narrow areas suit a badge.
Reviews and search results
The widget outputs review schema markup automatically. Whether Google shows a star rating depends on what the reviews are attached to — worth reading before you expect stars, because for a business reviewing itself the answer is usually no.
What does help either way: reviews on the page are content, and a page that answers what customers actually say is a page people stay on.