FB is as safe as anything else as long as you take sensible precautions and use the higher security settings. I do not accept friend invitations from anyone that I do not know in real life and would not post anything on there that I wouldn't say in real life. I think it is marvellous, and we have for example, a cousin's group on Messenger so that we can all keep in touch with family events and goings on, post photos of holidays etc, even though we are scattered all over the UK and beyond. There are lots of interest groups too that can be good to dip in and out of and we have a good one in the village to alert other people of road works or flooding or news about fund raising for local events etc, as well as selling stuff and posting help messages for missing pets and such.