Cryptocurrency is not a substitute for legal currency, and it can only do the same. The legal currency is backed by the government, and cryptocurrency cannot be replaced. The government will not allow cryptocurrencies to do so. The cryptocurrency has a large investment value, but as a currency, some of its characteristics may be detrimental to the transaction, such as high transaction costs, as well as the confirmation time and so on. This is why Bitcoin has not yet become a mainstream currency.