Is it possible to use the crypto currency for buying goods faster and safer? In my opinion, pull out ordinary paper money from your wallet and pass it to the seller much quicker than to find out from the seller the address of his digital wallet, enter it into your phone or laptop, carry out a transaction and make sure that it happened. As for security, here, too, everything is not so simple. A mobile phone or laptop can also be stolen, like cash.
As for the question of cash currency being squeezed out by crypto currency, here I agree that the crypto currency will significantly supersede the circulation of fiat on the market, but they will not be able to replace them completely.