You don't need a Google Review Feed - you need to understand why Google decides to show stars or not. both sites you listed have the same setup, same app, same structured data. One gets stars, the other doesn't. that's not a technical problem. that's Google's quality filter arbitrarily deciding one set of reviews meets their bar.
I've seen this dozens of times with B2B SaaS clients. same schema markup, same Shopify setup. one account gets star ratings in SERPs, the other doesn't. the difference? usually comes down to review volume, recency, and whether Google thinks the reviews are legit. if the site with no stars only has 12 reviews from 2021, Google quietly kills the display. Doesn't matter if the markup is flawless.
so no, you don't need a review feed. you need enough fresh, authentic reviews that Google trusts. everything else is just decoration