The application that they use says that it will erase the whole banknote or just a part of it based on the amount of purchase, but I haven't seen if these banknotes can be refilled, if it is used only once then I think it will be useless and will be too costly for the company to produce every time new banknotes.
From their faq:
https://tangem.com/faq << Redirects to Google docs.
Can I reuse a Tangem Note after extraction?
A Tangem Note has a limited number of transactions permitted, with the basic version limited to just one. Unless clearly identified as «reusable» in the validation app, you will not be able to use it after extraction at this time.
Can I extract partial value from a Tangem Note?
A Tangem Note may restrict extraction to only the full face value. You can currently extract a smaller value.
Technically they can be reusable but the business plan seems to be to make them in mass production numbers large enough so that they are cheap enough to be use-once disposables.