I would recommend them too. No problems in more than 5 years.

I am using mailbox too and am very happy with them.

In Germany the tap water has, by law, higher quality standards than bottled water. So yes, you can drink the tap water without boiling.

Signal and WhatsApp. WhatsApp only because a lot of people won’t switch to Signal (or Threema, or Matrix).

I use the same. In the Lemmy PWA I can just swipe right from the left side of the screen and this works as a back button for me.

Yes it does. You can follow BookWyrm accounts from Mastodon and Calckey. At least that is what I tested.