Yeah they claim on average webp can save up to 25% vs jpeg, but not sure if that holds up in practice, somewhat depends on the image. And if you're really interested in optimizing page speed, then I'm not sure making images 15-25% smaller is really going to do it. You'd be much better of lazy/late/on-scroll loading images below the fold rather than loading an entire page full of slightly smaller files.
I hear there is another new image format in the works, which will be open source and supported by all browsers, based on a video compression method that gets way better compression rates than webp, but it may not be available for another year or so.
