I helped my niece switch her number from M1 under her father's name to Vivifi under her name. Change of ownership is easy. When request for port in, need to scan owners IC also. OTP will be sent to the port in number to verify. Process was smooth.
I personally prefer to get the SIM card first and try out the signal etc before request for port-in. Eg if you collect SIM card at 2pm, can test for a couple of hours. Call, SMS, use data based on temp number. If satisfied, can submit port in request before cutoff time (can't remember exact time should be in late afternoon or evening), and port-in will trigger same night (except weekends, PH and eve of PH).
Just take note of 2 things :
1. Vivifi bills monthly. So if activate SIM card nearer end of the month, it is prorated to remaining days and can be quite tight to last till end of month. Feb is a short month so be careful.
2. Vivifi now has option to apply with myinfo or without myinfo. The activation method and time is different. So read up the difference before deciding whether to apply with myinfo or not.