Just switched from M1, here's my first impression of Zero1.
For the same price I am paying, I only had 40GB data on 4G, 100 mins &SMS on M1. I used to try out M1's 5G as well. On M1 5G SA, highest speed I was able to get was 647Mbps, in town area, on my iPhone 13 Pro.
I wanted to switch to their SIM only plan for $19.95 with 100GB data 1000 mins & SMS but was told "Bespoke is on the new system and cannot switch to old system". Whole lot of BS, so switched to Zero1.
Same price, 60GB with 5G before FUP kicks in, 500 mins & SMS. Did a speedtest, and results were pretty impressive for 5G NSA (still using the same phone).
313 Basement
Inside MRT, on the move and in the tunnel
Walking around the housing estate
Waterway PCN. The best result of all. This test alone had consumed about 2.6GB of data
Overall signal, well it's SingTel backbone. You can't go wrong with it. But somehow, it tends to flip between 3G and 4G at home, when I was able to get consistent 4G or even 5G SA with M1.
Customer service had so far been pretty good. They were quick to respond to tickets and ported my number over without a hitch.