I thought it was more using their router, especially over time. They charge $15/month for the router/modem which doesn’t sound too bad, but is $180/year on a device that retails for $180 or so. And they’ll happily keep charging that, forever - long past when their costs and a reasonable profit have been made.

They also force you to share your cable/wifi connection with other Xfinity users who are near you. Buying your own router and modem is a much better deal.