I don't see any disadvantage with CG-NAT. TPF gives CG-NAT IPv4 and Static IPv6 and I don't see any difference in day to day use when comparing it with Public IP while using Airtel. I am not sure why you are so adamant about getting a public IPv4 unless you are trying to access a FTP server or some IoT device while you are away from home, in that case you should opt for Static IPv4 from Airtel. Apart from that I don't see any real benefit of public IPv4.