Hi Sam,
My Judge.me Product Reviews app has a preview badge for collection pages that shows, for each product, the number of reviews and average star rating.
The preview badge is available in my free plan and installation instructions are available in the FAQ. If you upgrade to my paid plan ($15/month) you can customize all the settings and I'll help you install the preview badge.
Note that my app also sends review request emails, which increase your sales compared to using the Shopify Reviews app which doesn't send review request emails.