What if it only works 75% of the time? Let's say you eat a meal, and just when you go to pay, the restaurant looks at this crazy thing and says "no, you can't use that". You have to carry another card with you, or cash to cover any purchase you might make.
It's only good if it works as well as credit cards work - 99.9% of places accept them.
It's only good if it works as well as credit cards work - 99.9% of places accept them.