TL;DR: It works as advertised and is well worth the price.

Long version: After a bit of testing, I'm quite happy to replace Autoptimize / Shortpixel + local page caching plugin with EWWW IO & SWIS going forward. EWWW IO has most of the options of AO/SP, and some more useful options that are unique to EWWW IO.

File sizes of optimized images, on average and in our usage scenario, are slightly larger than ShortPixel (using glossy setting in ShortPixel with loseless image quality in AO CDN settings). However the image IQ from EWWW IO is far superior (IMO) and is worth the few extra KB. CDN speed seems as good, if not better, with incidental testing.

There's a few options in AO that I wish EWWW would add (Remove WP emoji bloat, remove query strings from asset URLs, optimize HTML via minify and comment removal), but there's also more options available in EWWW that can be quite useful, which are missing in AO. Most of the missing options in EWWW IO can be handled via theme functions.php, or another plugin that we regularly use (Code Snippets).

SWIS, with local page caching, is icing on the cake. SWIS also provides the capability to dequeue specific unnecessary assets (CSS/JS) via a nice interface, and can be controlled at the page level. This makes it dead simple to gain at least a few point boost in page speed ratings.

These two plugins replace the functionality of four separate plugins for us. I like it when a new tool makes certain tasks simpler.

Lastly, we had a week long interaction with support. During that time, I was provided two custom plugin builds to debug/resolve the issue. There's not many developers that will provide you with an updated plugin build for testing, outside of regular release channels. Impressive all around!