With regards to ADSB, we only see what they want us to see. Even the Russkies left theirs on a couple of days ago when they practiced their Doomsday escape procedure.
Agreed, "B-52 engines running" might be a bit too much info, but five minutes later they are there for everyone to see anyway.
I do believe the people at the Home Office would be onto these groups like a shot if it was becoming a problem. Hell, they could probably black out social media for a few hours if they needed too.