增值開或續plan好似貴過換新咭 -> seems truth but you forget your need to keep main no. in other SIM -> there will have a cost -> so single SIM may not be expensive than using dual SIMs
多人用,死機風險較高 -> More/ Lucky mobile, few people used means low risk
Anyway, choose the ways you feel most comfortable to use eg. ClubSIM ($28 unlimited) + 2nd Data SIM over 50G