To me, the answer is:
1. Go for a mix of "3rd party reviews", including Google reviews and other reviews.
2. Don't forget to also solicit "1st party" reviews - reviews given to you directly by customers. They have business value and also SEO value when used on your website correctly.
What is especially valuable with Google reviews:
1. They appear to be significant factor in SERPs rankings.
2. They appear visibly in SERPs and often that influences others to select businesses that show up in SERPs with lots of review stars and review counts.
3. Other reviews appear less visibly in SERPs and so may be less influential in getting searchers to choose your business.
4. They appear prominently in Knowledge Panels.
To be honest, what I am trying to do is find a justification for paying for 3rd party review services. They cost $$$ per month and yet I struggle to find the value in them compared with simple Google Reviews.
One advantage of course is 3rd they are "cross-platform" in the sense that they can be transmitted (via Rich Snippets for example) to search engines other than Google. But that seems like a relatively minor advantage really.
Great question! Garrett here from Grade.us (Tim, thanks for the mention!)
The reality is that reviews are hard to earn. A platform like ours helps automate the review request via email and text campaign drips so it's one less marketing process for your team to manage.
The benefit of the review funnel is the ability for you to not only distribute reviews across multiple sites beyond Google (Facebook recommendations, industry specific review sites), it provides options for your customers to leave a review on the site they're comfortable with. They may have never written a google review, but they're comfortable recommending your business on Facebook.
New advertising option:
A review of your product or service posted by a Sterling Sky employee. This will also be shared on the Sterling Sky & LSF Twitter accounts, our Facebook group, LinkedIn, and both newsletters.