I'm trying to decide if I should upgrade or replace my cable modem.
The one I'm using now is provided by TWC: Motorola SB5101 Surfboard Cable Modem
It works fine, but I would like to save on the leasing fee. So I was thinking of replacing it with
my own Motorola SB5101 Surfboard Cable Modem which I used before I moved.
I would have been using it already, but it wouldn't register for my account.

The modem was previously used with a family members account when I lived with them. It's been over 5+
years since that family member (past away) had a TWC account. Should I be able to register my modem now?
Or would I be better off with one of their other preferred modems? Which one?
Cable Modems:
Motorola SB6121, modem only, IPv6 ready
Firmware version - 1.0.6.8-SCM01
Motorola SB6141, modem only, IPv6 ready
Firmware version - SB_KOMODO-1.0.6.14-SCM01
Motorola SBG6580, modem & WiFi, IPv6 ready
Firmware version - SBG6580-6.5.2.0-GA-06-077-NOSH
Motorola SBG6782AC, modem & WiFi, IPv6 ready
Firmware version - SBG6X82-8.5.0.0-GA-05-15-NOSH
ARRIS/Motorola SB6183, modem only, IPv6 ready
Firmware version - 9.2.0.0-GA-03-29-NOSH
As I think of this even more the old saying "If It Isn't Broke, Don't Fix It" comes to mind.
What would you do?
Stick with what's working?
Give there's back, replace with mine?
Give there's back, get a new one?