If a company uses more than a cloud service on which they run their platform, you don't need to use a different service to manage secrets for each of them, instead Conjur bundles all of them in a simple to use user interface.
The official documentation of Ansible vault does a great job at explaining how Ansible Vault works and how to use the easy UI for encrypting, decrypting, and re-keying your secrets for storing in source control.
Box provides dedicated hardware (HSMs) that the enterprise has complete control over and can provide access to Box in a granular way with Box in turn providing cloud services such as deduplication, search indexing, information rights management, etc.
Amazon has used a lot of techniques to harden the process of storing and securing keys in its service. For example, keys are not stored on disk, nor are they allowed to persist in memory. Amazon employees can not access a user's secret keys physically and the keys themselves are stored in the...
Red October uses its own crypto implementation in to encrypt secrets. While it's not necessarily a security risk, it would be safer to use a crypto library that has proven it's worth and that has been used for a long time in a lot of projects.