I have looked into this briefly. Several modules seems to use the script at
https://github.com/rosell-dk/webp-convert. And that seems to be a good script.
I noticed that when 'ETS Super Speed' release an update to their module, the haven't updated webp-convert to the latest release.
But it seems that 'Image: WebP, Compress, Zoom, Lazy load, Alt & More' use an up-to-date version of webp-convert.
Latest version is available at
DEMO HERE Overview Greatly improve your SEO and Website Speed by using Google WebP, Compressing images , Lazy Load and generate ALT TAGS for your images. What this module does for you Speed up your website IMAGE COMPRESSION FOR ALL THE SHOP IMAGES, INCLUDING CUSTOM MODULES/THEME GOOGLE WEBP...
www.nulledfrm.com
I can't really tell you how good it is thou. I haven't tested it that much.
I'm thinking about doing a hard coded script that fetch CDN images from Sirv (sirv.com) and store them on my local sever. But I'm not sure if the quality/compression are better on Sirv than using a module with webp-convert.