It has limited security value (basically guarding against someone walking out of the data center with a hard drive). However it is extremely simple to use when AWS supports it and great for checking off compliance boxes ✅.
Your example would be closer to column-level encryption or something like that.
Generally encryption at rest would be more along the lines of what AWS can do for you: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/EncryptionAtRest.html
It has limited security value (basically guarding against someone walking out of the data center with a hard drive). However it is extremely simple to use when AWS supports it and great for checking off compliance boxes ✅.
Your example would be closer to column-level encryption or something like that.