Filestore is basically a single google-managed instance running NFS. It's much less sophisticated and resilient than EFS, but also can be much faster since it doesn't have the overhead of a distributed system. Don't try running something that touches lots of files like mercurial on EFS, trust me...
The article says Elastifile (which I know nothing about) will become part of filestore.
Filestore is also really expensive for what is basically just NFS.
Managed services are generally for enterprise, where you're fully costing out support + security mitigation.
Eliminating team coordination tips the balance.
EFS is... surprisingly cheap, as long as you don’t need heavy sustained IO for more than a few hours at a time. Great for a simple file store and some big data purposes.