And after a few weeks of seeing what they're doing on Facebook, commenting and posting as I thought appropriate (and still being at the followers / likes/dislikes = 0 level) my conclusion is ... it's total rubbish. It's badly laid out, it's high speed banality (you do get quick responses if you ask a question). It's as though adults have taken have taken up childrens playground games and are trying to convince themselves they're meaningful. I'm still there at the moment because of the novelty + I've got Covid time on my hands, but the adverts and the restrictions are chipping away at my resolve already.
I very much doubt I'll be there long term because there's nothing to keep me. Maybe there is a more serious (in the sense of being worth the effort) side to it but if there is I haven't come across it so far. I suppose I could just sign up for another 50 groups but that would just make it a mile wide but still only an inch deep.
Maybe my occasional presence there adds to Facebook's coffers through counting me as an advertising recipient but if it does the advertisers are getting poor value for money.