Current parameter store user - one feature not mentioned in the comparison is the fact that accessing / updating a secret in parameter store will show up in Cloudtrail. Is there a similar audit trail in strongbox?
For Strongbox CloudTrail logs are indirect: you need to look at the logs of the backends used by Strongbox, i.e. KMS and DynamoDB. Consistent naming of the resources (managed by Strongbox) should help you filter out the correct entries.