Sorry to ask ... What's the black ONT box ?is it new and any difference compare to the white one ?
Yes.
White ONT has the word "Nucleus Connect" (NC) which means you are using Starhub's subsidiary network. Hence, M1 will charge you $2.10 monthly rental for that since it is not in their business interest to stick with NC as they have become an Op-Co itself.
What it means is that while both ONT are technically capable to handle 1Gbps plan as Starhub and M1 do have such extreme plan, M1 will not subscribe more lines with NC and hence you can only stick to your plan if you choose not to move on with M1's black ONT.
The advantage to move to use M1's black ONT is that when sh!t happens, you can safely blame M1 or OpenNet aka Singtel as chances are will be a 2 way tai-chi party. But if you stick to White ONT, then NC, M1 and OpenNet will play tai chi and you will be in the losing end.
However, the disadvantage is that a change of ONT will involve port 2 as if you jump ship from Singtel to M1 as an example. Then, OpenNet may screw you deeply as the capacity issue is a real pain in the back. Hope after OpenNet's appeal the IDA's $750k fine (If ever) will become $7.5 million instead of giving the screwed up attitude.
IDA fines OpenNet $750,000 for failing to comply with service obligations and standards
Recommendation: If you are going to stay with M1 for long, move on to M1's black ONT despite potential inconvenience and the monthly fee could be a pain in the back.
However, if you plan to switch to MyRepublic or Starhub after end of contract, then don't move to Black ONT liao.