Facebook Groups is the most effective bait and switch tactic. No surprise that MZ announced Groups as their priority this year. First, they get enthusiasts to start interesting groups and attract members - it works well initially, because a new group is generally given a boost of viewership - most members actually see the group posts in their feeds. Once the group grows, the FB Smart Feed starts to reduce the number of members that get updates in their feeds - and surely most of them never ever visit the group page itself again, because it doesn't look like anything is happening. Then, they require group or pages admins to "boost" their posts for a fee to be able to reach their group members! This is an outrageous tactic - which clearly means that the Ai behind smart feed is not selecting most relevant posts for a user, rather it selects the ones that ultimately lead to more group admins boosting their posts.
Then, there's a risk of losing your group entirely at any moment - all it takes is one member posting something FB admins don't like and it's gone - good luck reinstating it.
There is no way of "exporting" your group members in any way either - you can't just grab their contacts and reestablish the group on some other platform.
Running a FB group is like renting a room in somebody else's house where you have to pay every time you want to call your friends AND you can be kicked out any moment without prior notice.