I'm afraid this is just as "free" as an adwords ad that is never clicked. It sounds like it's free, but behind the scenes Google runs a CPM auction based on cli

I'm afraid this is just as "free" as an adwords ad that is never clicked. It sounds like it's free, but behind the scenes Google runs a CPM auction based on click (or view in case of video) rate and the conversion of CPC to CPM. That means if you get a very small number of clicks or views, your price per click or view goes up accordingly.