Yes - REST calls are fully supported, along SDK’s for with Swift, Java, ObjC, C++
Not advocating by any means but we really like the simplicity of implementation for the Firebase Storage product. Once the pod file and project is updated, uploading and downloading files are just a few lines of code with no real struggle to add it to an existing (or new) project.
The issue we had with S3 and Stitch is the amount of hoops we went through trying to implement it (not REST) - after months of effort your team determined that the Stitch SDK isn’t supported (and doesn’t work) on macOS and they “have no plans to make it work on macOS”
There are also a number of issues with iOS and were finally told we should stick with REST (which is not part of our project implementation). So it wasn’t a solution for us.
However, for any projects relying on REST, it seems to be a smoother ride.
As a side note - it would be pretty awesome to have a connection to AWS S3 and cloud storage directly from MongoDB Realm SDK.
Just my 02. - your milage may vary.