Are you sure they’re charging you for the modem and not the gateway/wifi features it comes on the device?, I’m almost certain they will lend you the modem at no cost of your internet plan and you can add your own router, their routers should have the capabilities of handling the internet speeds they sell, but generally speaking as all other comments says docsis 3.1 is the bare minimum any any with this compatbility will offer you speeds, WiFi and accessibility of managing your network would be best from a router vs modem tbh