In my opinion its better to take backup of Office 365 using third party backup as well, so that even any users who are using office 365 leaves your company, backup will be protected which are used by that particular users and you can restore at any time as your schedule.
Actually, I am a technical person so I look only at the technical part rather than the sales part. So I don't know what the prices are for Veritas appliances and software licenses. But the licences of NetBackup are available on both storage and per virtual machine-based.
RPO and RTO is the most important thing while taking backup and recovery software and I usually prefer to secure the date on its own file system during the backup for security.
