Hi Jen!
Yes, this is in place of purchasing ink cartridges. They send you the cartridges in the mail whenever you start to get low. You can then login online to see how many pages you’ve used so far that month, how many rollover pages you have or change your plan. I often will switch to the cheapest plan for months when I’m not printing much and then bump it back up to a larger plan for a month or two when I need to print a lot.
Hope that helps answer some of your questions!

I have had to reconsider some of the free printable just for this reason.

Thank you!