I wrote a pull request for this add-on. The source code looks safe to me. The maintainers were friendly and helpful. The add-on itself is very useful and configurable.

wont let me access my google apps through my school Microsoft acct? weird and a big hinderance to my work

je ne sais pas
car malheureusement tourne en boucle à charger des onglets sans avoir aucun résultat autre que devoir rapidement désactiver ce module

Breaks back button when linked to google or youtube

Works well. The addon doesn't support .google TLD itself so some of *.google sites (e.g. https://opensource.google/) is loaded in a usual tab even if I entered the address in Google container tab.

Worked fine for a while, but something changed very recently where every Youtube link opens in TWO TABS. Super annoying...so buh bye Google Container.

I wish I could whitelist a web site to easily use "Login with Google" where I want to. For the moment, I need to disable this addon.

Not great. Can use google for the most part but can't login to my university email using this. After being redirected from the university portal to what I assume would be gmail, it gets stuck at "www.google.com/a/.edu/acs"

Was a bit concerned when google started to sync my clipboard across devices. This fixed that, and hasn't broken any sites that I've tried (sheets, drive, gmail, youtube, search) with the default configuration.