Actually, ALL ad supported models work by paying consumers to look at ads. It's why broadcast Tv and radio are " free". Free-mium games work on the same principle. The KSO model has worked quite well- so far. Other models may also work.
As I said, the special offers seem to be tailing off for the KSO. And no new big-name advertisers seem to be jumping on-board. You say; "worked quite well," I say; "pretty much tapped out."