Excellent tool.

Pros
- JS / CSS served with Gumlet
- Fast AWS CloudFront CDN
- Video optimization coming soon
- Simple.
- Replaces 3 Shortpixel plugins with single Gumlet plugin
- Replaces lazy load plugin (so single Gumlet plugin instead of 4)
- Better quality and faster CDN than Shortpixel
- Good support, quick replies, helps online, fix issues quick
- Background images work now
- Special characters in filenames work now (non-english)
- Pinpoint images with CSS class if no Gumlet optimization needed
- Doesn't alter images
- No request limits (serve millions of images if needed)
- supports jpg, png, gif, SVG and webp
- analytics about the usage
- white label option if you go full 1TB / month
- has more pops (AWS) than Shortpixel (Stackpack)
- control cache timing

Cons
- There was lots of issues when this deal landed on Appsumo, but they have been actively fixing the bugs with good results so far.

Here are some sites using Gumlet (other sumolings)
https://ThatLTD.life
https://www.wpguy.de
https://Raindrop.io
https://puretruthson.com

https://bit.ly/2uEHjuH
http://prntscr.com/qo6vpy

Image quality comparison Shortpixel vs Gumlet (link of another Sumoling)
https://www.notion.so/wpfy/SPAI-VS-Gunmlet-453a0081574e4b43b7dbd89cadf3f757

Some other sumolings reviews
https://youtu.be/4g1A9XLhTn0
https://www.youtube.com/watch?v=1PVnuuKcczk

Great value for the price. Get your page ranked and get better UX on your site (speed).