It works to buy darknet drugs, sure. Wake me up when I can go to the grocery store and buy some peaches. "Don't worry, cashier-bro, the transaction will only take 20 minutes to go through, trust me!"
It does work for groceries, although not at a physical store, because the store is controlled by government henchmen wrt to their payments. Fwiw, one can trivially by an Amazon gift card using cryptocurrency, using which one can then pay for online groceries.
As for transaction confirmation times, there are cryptocurrencies in common use that confirm nearly immediately. The lack of your knowledge shows.
There are so many valid criticisms of crypto, but transaction confirmation time has been solved a long time ago.