I think the key benefit brushed on by this article is the potential 10x improvement in access speeds (which has many applications, beyond reducing your s3 op charges).
> S3 Express One Zone can improve data access speeds by 10x and reduce request costs by 50% compared to S3 Standard and scales to process millions of requests per minute.
10x reduction in latency, higher storage costs with lower access costs (SSD instead of spinning disks). So high I/O, small files situations (with no need for cross AZ access) are where the benefits can be found.
This will work great with the s3 mount point that AWS recently released. This will outperform EFS if your application does not require full POSIX compatibility.
If it's only a cache it should be on EBS, which is still way faster and 2x less expensive.
I started a migration to s3 for such a project (container image caching) but then stopped when I realized what I was doing.
Yes, EBS is the gold standard but managing a EBS to scale up and down instantly, be available to multiple instances, lifecycle management, managing replica, switchover etc. are definitely not easy. And EBS are bad choice when throughput needed is very spiky.
> S3 Express One Zone can improve data access speeds by 10x and reduce request costs by 50% compared to S3 Standard and scales to process millions of requests per minute.