Easy to use a non rented modem. Unlike fuzzytone’s experience everyone I know who has swapped rental modem out has never gone back. Maybe 10 people so just shows how a small sample size is problematic.
Modem compatibility is easily verified on Comcast website or even Amazon. I currently own a Motorola MB8611 and am on Xfinity ie Comcast cable. Much easier to swap out and get working than before. All done online via their app. Oh, don’t buy a refurb as often those MAC addresses show as still in use and are a real pain to get authorized.