100% agreeing with NotFuzzyWarm on this one... Testnet isn't created to be secure, or a store of value... It is created to test.
And if you use it for the purpose it was created (testing), it does a good job.
Use testnet to test out new wallets, new scripts, spend, receive, create paper wallets, create an airgapped setup, test out the payment gateway on your new service. Afterwards, either keep the tBTC or give it away, as soon as your tests are done, there's no real use for the tBTC anymore.
Do realise that having zero value does not mean it's free to mine the tBTC...