It's a project by among others Q (@q@glauca.space on mastodon), a well known hacker in the CCC sphere of influence. She held some very interesting talks and I use another Project of hers (zügli.app, extracting info from train tickets) every day.
I wanted to use it myself but in the end it was simply cheaper to register my domain elsewhere.
Trustworthy: I think so
Customer support if something breaks: They seem quite busy and this is more of a side project, so be patient
I've got a cheap VPS to act as a relay with a static, more or less trusted IP address. It just forwards incoming mail to my homelab, and outcoming mail to the recipient. The setup can get pretty complex if you haven't done this before.
Would probably be a lot easier to just deploy addy to a vps and call it a day
Can't recommend https://addy.io/ enough, I have been selfhosting it for some time now and have not had any complaints
Really? Which Protests do you mean? The vast majority of German flags I saw on anti Nazi demos in Germany had been mounted to Buildings or the hands of some Nazi Idiot at the counterprotest.
Going one step towards the center of the political spectrum from the firmly left learning anti Nazi Demos, there are the anti AFD Demos which also attract(ed) people with far more moderate centrist political views than the average Antifa member, thus being more likely to support the idea of the state of Germany in its current form. Still, most flags you'd see were for pride / lgbtq+ or political organisations.
You might see a German flag from time to time but i think it's just plain wrong to call it common.