You can send a used Roku device that's linked to your account and any subscriptions you have through Roku would be available to them. Bear in mind that any purchases or subscriptions they make will be charged to whatever payment method that's attached to your Roku account. In addition, any channels/apps they add or remove would be added or removed from all Roku devices linked to your account. Any subscriptions you have directly with a provider (e.g., Netflix, Hulu, etc.) that you've already signed into would also be available.
I'm not trying to give any advice on whether this is a good idea or not; just trying to let you know how things work.
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