I suspect Kinsta’s Edge Caching is just Cloudflare For SaaS offering up to their customers features available to Kinsta’s Cloudflare Enterprise account? As such they probably build a customer focused custom Cloudflare Worker for edge caching. One thing that APO does that regularly Cloudflare Worker caching didn’t do in the past was Tiered Caching Tiered Cache · Cloudflare Cache (CDN) docs.
But now Cloudflare has opened up Tiered Caching to all paid Cloudflare plans anyway.
One possibility is that Kinsta hasn’t enabled on their Enterprise plan’s Cloudflare For SaaS’s Tiered caching - opting to prioritize Cloudflare Bandwidth Alliance over Tiered Caching Tiered Cache · Cloudflare Cache (CDN) docs as Kinsta uses Google Cloud for their hosting and egress bandwidth is expensive!
So taking advantage of Cloudflare Bandwidth Alliance with Google Cloud Bandwidth Alliance partner host Bandwidth Alliance | Reduce Data Transfer Fees will save Kinsta a lot of $$$$ and only way they can really afford to price their plans the way they do I suspect? This is all speculation on my part though.
Only difference will be without Tiered Cache enabled on Kinsta Edge Caching, performance will be slightly behind Cloudflare APO for some geographical locations for cache misses Tiered Cache · Cloudflare Cache (CDN) docs
Smart Tiered Cache
Smart Tiered Cache dynamically selects the single best upper tier for each of your website’s origins with no configuration required, using our in-house performance and routing data. Cloudflare collects latency data for each request to an origin, and uses the latency data to determine how well any upper-tier data center is connected with an origin. As a result, Cloudflare can select the best data center with the lowest latency to be the upper-tier for an origin.
Easiest option is try both for a month or two and decide which is better for you, APO or Kinsta Edge Caching.