There are two systems(?) for these cards- EZ-link and CEPAS.
NETS is associated with debit/credit cards and mostly used in retail, and EZ-Link cards for transport. They currently aren’t interchangeable and you need different cards for both functions. You can purchase CEPAS cards which have both the NETS and EZ-link function, but ezlink cards are only partnered with NETS in certain places, mostly partnerships with hawker centres/ school canteens for students.
TL;DR:
If you’re a tourist with a temporary ezlink card, it’s unlikely that you’ll have the NETS function. It also won’t be very useful since not all hawker centres (usually only air-conditioned food courts etc.) allow you to pay with NETS. Stick to using Monzo and cash 