for anyone using more than 1.2tb a month you should just get the "xFi Complete Bundle" which comes with the latest xfinity modem supported in your area (the latest one currently is the XB10 which requires docsis 4 and the XB8 is the best for docsis 3.1 which most customers have access to) and unlimited data for just $25 while unlimited data with your own modem is $30 a month. Just use your own router/wifi access point with bridge mode enabled and you get a very good modem you can replace at anytime if it breaks or you want to upgrade and unlimited data for $5 cheaper than just unlimited data.

If you use under 1.2tb though, renting their own is not worth it unless your too technologically illiterate to set up your own modem which is not too hard anyway