Hi @m-n-a ,
This is Ellie fromBOGOS.io Free Gifts 
“Judge.me Product Reviews” on Shopify App Store may be the app you are seeking for to put rating stars next to your products, and yes, it’s FREE.
This is how it displays:
- On website
- On mobile phone
It also provides many other free essential features for you to discover.
These are my recommendations. I truly hope it helps!
Wish you all the best with the business 
Ellie