(I work at Netlify, and worked on this)
It uses Deno Deploy for the actual execution of the function, but the whole workflow around it, routing and middleware API, integration with frameworks and the CDN are all Netlify. It's similar to how Netlify Functions use AWS Lambda for execution. It does add latency, but it's tens of ms, because it uses Deno Deploy nodes that are very close to the Netlify edge nodes. Deno Deploy is awesome, but Netlify has a much more complete platform, so the combination is best of both worlds.