Had friends over who were laughing at me because their Roku TVs don't require a box (or the monthly fee that comes with it), because they have Comcast. Comcast has a Roku app that allows its customers to stream content! As it stands now, we are paying for 2 min-boxes and need a third for our kids' room. The cost to rent all those boxes really adds up! I will be switching to Comcast after our agreement is up, if they don't come out with an app of their own!
Yes it is free.
But a couple of things to keep in mind.
Comcast app does not support on demand (even free content)
With Comcast, it appears you have to pay extra for DVR service.
FIOS includes in STB service costs.
FIOS DVR is local vs cloud. To some that is a plus as your content works even if your TV service is out.