There's a few reasons to link Rokus to the same Roku account. One is that anything purchased through Roku is linked to the account, not the device, so it's available on every device linked to the same account.
The only way to have different channels/apps on different devices is to link them to different Roku accounts. If you don't subscribe to anything through Roku then you may as well create another Roku account and link your stick to the new account.
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