I think it wont make the slightest bit of difference, Also, new blood can be good - stirs the pool.
Those that use it to sell guns instead of FB will just post adverts I suspect. The inane stuff will still go on the larger FB groups.
Personally, I filter all the adverts out on here as Im personally not interested in buying or trading RIFs, so you only have to see them if you want to.
A lot of people are over-reacting to this FB restriction because they havent read properly.
Its only affecting secondhand sales and trades and FB havent banned airsoft. Sometimes their bots get a bit overenthusiastic and ban somebody because it misunderstands the post. There are some very good groups on FB, not just airsoft related ones.
Groups and forums are about people. FB is just a medium, a carrier, for peoples thoughts.