Any one who operates a VPN has the ability to monitor and record all traffic through the VPN tunnel.Even traffic that is previously encrypted can provide traffic source and destination information. As a result, the only 100% trustworthy VPN is one operated by the enterprise you are connecting to. My company provided PVN service for all external employees for us to access the internal networks and servers. Of course they can and do monitor traffic, but who cares, because they are protecting the enterprise, not the individual employees.
So, now we move to third party VPNs, such as the FaceBook offering. These services protect us from rogue or open networks such as found in every coffee shop. Can we trust the VPN provider not to decrypt and monitor our traffic, or not to maintain a metadata collection on all we do? Maybe, maybe not, for a generic third party, even if they charge.
On the other hand, any VPN offered by FaceBook or Google, whether free or paid, is guaranteed to be mining every bit of data out of your traffic they can. Both companies have already shown that to be their business model. Trust them to guard your privacy? No, not at all.