It's still good to test the main backup - untested backups are not backups.

Which reminds me, I should test our backups again...

Sure, but who is going to pay for the multiple backup sites?

The whole point of having an Artic seed vault is passive failsafe: "Even if the power were to fail, the vault would stay frozen and sealed for at least 200 years."

As a nice benefit, since it's passive failsafe, it's also cheap to maintain.