Eh -- "secure-ish" at best. Spending those utxo's requires revealing the pubkey, at which point someone with a quantum computer can just break your pubkey and

Eh -- "secure-ish" at best. Spending those utxo's requires revealing the pubkey, at which point someone with a quantum computer can just break your pubkey and offer a new transaction with a higher fee while your transaction is still in the mempool.