What are "the three"?
archy
For me paru, but never tried Aura
There is an interview with the founder on one of the Privacy podcasts. You can form your opinion. My opinion - yes, they are trustworthy and you can do with them anything that you can with any Linux box, alternatively flash a clean OpenWRT for extra paranoia
Signatures are different. Uninstall old FDroid version first
I'm not your buddy, bro
look on XDA developers forum for your model. They usually have plenty of alternative ROMs
Using Soundcore with their app and internet access denied. Set up once, deleted the app
I don't think you pay for the iOS app, only the server portion can be licensed AFAIK
I use FreshRSS - really nice app, using PWA on desktop and a plain bookmark on the tablet
How did they find out???
Alias description? Inbox headers?
Looks like you already did
Google it