This means that all of the non-atomic operations that you might want to do on S3 (including edits to the middle of files, renames, etc) are run on the machine running S3fs. As a result, if your machine crashes, it's not clear what's going to show up in your S3 bucket or if would corrupt things.
As a result, S3fs is also slow because it means that the next stop after your machine is S3, which isn't suitable for many file-based applications.
What AWS has built here is different, using EFS as the middle layer means that there's a safe, durable place for your file system operations to go while they're being assembled in object operations. It also means that the performance should be much better than s3fs (it's talking to ssds where data is 1ms away instead of hdds where data is 30ms away).
The purpose of S3 isn't to be cheap, it's to be simple.
I thought that would be their https://github.com/awslabs/mountpoint-s3 . But no mention about this one either.
S3 files does have the advantage of having a "shared" cache via EFS, but then that would probably also make the cache slower.
Reading through it, I was only thinking "is this distinguished engineer TOC 2M aware that people have been doing this since forever?".