The main difference is that the My Number system is basically the equivalent of a U.S. Social Security Number, in the sense that the number will be potentially

The main difference is that the My Number system is basically the equivalent of a U.S. Social Security Number, in the sense that the number will be potentially integrated with things like taxes, pension, bank accounts, health records, etc. This obviously has some conveniences, but also carries more risk. Naturally, losing your card is much worse than losing a basic ID card. Also note that the 12-digit My Number sticks with you throughout your life, unlike an ID number that can be changed. So once you obtain someone's number, they have no easy way of invalidating it so that you can't use it.