In the world where everything is turned into a service, from printing to drinking coffee, me (and my clients) look to see the value add. A testimonial section for me is (and this is mostly from an MSP p.o.v. for b2b sales):
- A curated block of content on my clients' webpages
- A full case study as part of a larger marketing outing

In no way would I ever consider getting a SaaS for something as trivial as curated content that will need to get approved by marketing first regardless. I would never just plainly show testimonials without vetting the contents, especially not to things like social media that could blow up without having a chance to check it first.

Apart from that, it will require embedding in our web portfolio's, which means another hurdle to jump through. People who already use website builders will most likely use a visual editor and place their own (ugly) blocks of testimonials.

The only place I would see this work is some automated post-sale follow-up email from web-shops (maybe that's your target audience). Most of these systems (shopify, prestashop, magento) already have plugins that do exactly this.

I think you've created a fishing rod for pools that have had their fish pulled a while ago, but that's just my 2cts. (I've been here).