Optimised Images
Left image is directly from the server/Cloudflare as a .jpg 800px wide. 122kB
Right image is saved from seo.web-cdn.org as a .webp 800px wide. 40.6kB
There's a huge difference in file size in this case. I'd say there is a noticeable difference in quality. However, oddly, the webp is one pixel less in height which means the browser must be squashing it and therefore the comparision isn't possible this way.
So below I've added them in a better way to compare. There is a difference in quality, but it's not much considering the huge saving in file size.