In addition to your points, I can't figure out the licensing - they state that CheerpX is a commercial product, but I am unable to find any information about paid or free usage tiers... Or maybe I just didn't dig deep enough...
Licensing
Cheerp is free open-source software, actively developed and maintained by Leaning Technologies. Commercial support, feature fast tracking, sponsored development and consulting packages are available for Enterprise customers.
https://cheerpj.com/licensing/
The X version seems to be minified CDN hosted .js file but no other info about usage. The only comment in the file indicates that its some sort of C/C++ file presumable ported over to JS
/Compiled using Cheerp (R) by Leaning Technologies Ltd/