just buy your own simple modem and install your own wireless access point.
do not buy any device from comcast you dont fully control!
Also make sure your phone and other every day carry items never connect to the Internet via your ISP’s network or emit radio signals while nearby your home.
Until the day when to use the service you have to use their device. Or it's being used at work, a hotel, in stores, in your kids school, or anywhere you have no say on the devices used.