On Metal NFC Tags are not available in most time. Only when your contactless application involves attaching NFC tags to metal surfaces, you will need to use it.
As we known, NFC chips and antenna are with sensitivity, so they are susceptible to interference from metals in close proximity. This could corrupt the signal, rendering your tag less reliable or even unusable.
By incorporating a shielding layer, it can protect the chip’s Contactless signal on Metal NFC chips. Thus, On Metal NFC Tags are necessary for your program.