What has a bitcoin debit card to do with the way you store your fiat money? If you are concerned about the security of banks and you do not want to change to btc or you need some fiat for purchases you can take the cash and put it in a vault at your place.
Holding government currency ensures that you lose purchasing power over the long run.
Converting immediately to bitcoins is best, and holding your money in bitcoin as long as possible is even better.
The fact that this Mastercard converts to government currency only at the point of sale means that you can hold your money in bitcoins for the longest possible time, just as long as making a purchase using bitcoins.