To name a couple:
1. IPV6 does not work with CC.
2. Can’t use WIFI calling and send/receive pictures.
Both completely useless. Especially IPv6 since your modem always gets an IPv6 address anyway, there's no need for IPv6 on your local network. As for wifi calling, if your service sucks so bad you need wifi calling... get a different carrier.
Luckily for me the R1 is working