This is a fully functional cable modem that I have been using for my internet connection with Comcast/Xfinity.
It complies with the DOCSIS 3.0 standard but the maximum speed you will get is 150 Mbps on download.
If you have the basic plan from Xfinity and pay for their equipment you should get this modem.
It comes complete with the instruction manual and power supply. I can guarantee that it works fine.
You will need to leave me a cell phone number so we can text to find a time slot for you to come pick it up.