The data saver extensions like Opera's and Google's are becoming more and more useless, why? because everyday more websites are moving towards the HTTPS protocol and those data saver extensions can only work with HTTP websites. also Google prioritizes websites using HTTPS and puts them first in search results. right now All popular and unpopular social networks, big data hosts are using HTTPS. also I tried them a lot on both Android and desktop, they cause a lot of problems with websites and their UI, mostly render websites unresponsive.
This is an interesting idea, thank you @Boonierat. I am sure that there are many others that are worried about data caps, and are also looking for similar solutions. I will take this feedback to the folks who run services. Thank you for your feedback, Elliot