As per the screenshots, it's essentially like local data that rolls over to the next month instead of being forfeited, allowing you to accumulate what you don't use to the next month.
I have been on the Singtel Hi! 4G plan for two months now, and it’s honestly one of the best I’ve used. The coverage is solid, and the 4G speeds are impressive—hitting
100–200 Mbps outdoors, which easily beats Starhub and M1 in my area. Most importantly, the roaming coverage is extensive and the data allowance is generous. As long as this plan stays around, I don't see myself needing to buy travel eSIMs anymore.