Comcast themselves used the older version of that modem. No way it doesn't work. It's Comcast certified. If you won't miss the 10, get the kit, but you will end up:
A. Setting their equipment up, taking it out for yours, then returning it and got beat for 10 dollars,
OR
B. Get the kit, set yours up like I said and got beat for 10 dollars.
Not to mention, they may stick you with the equipment rental fee, even if you go right to your modem.
I would not do online, and try to get by the fee, but that's me