Getting it right
If you sell products, this is a real promise. A product page carrying a star rating and a count in the search result is measurably more clicked, and the markup goes out without you configuring anything.
If you are a local or service business, be realistic. Your stars already appear where they count — in Maps and the local pack, from your Google Business Profile. That is the asset worth building, and it is not something a widget on your website produces.
How to tell whether it worked
Search Console shows whether Google picked up the markup and whether it is showing a rich result. Validation and display are different things: correct markup makes a rich result possible, and Google still decides.