Can I Buy A Digital Adapter For Comcast -

“the product is 100% useless. Product cannot be used by Comcast/xfinity customers because the company has the power to activate the unit at which time they will bill the user a rental fee.” eBay Available Alternatives

Comcast requires all devices to be activated on their network to function. Many off-market adapters are reported as "useless" by buyers because the company may refuse to activate customer-owned adapters or will still charge a monthly rental fee if they do.

Digital Transport Adapters (DTAs) are designed only for standard channels and do not support premium content, On Demand, or DVR features. Community Feedback

Users on community forums often warn that while the hardware is physically available, it is frequently a "paperweight" without official service authorization.