I think the question you should ask is "what is the impact of transition from ad-free to include ads in players?"

All examples I personally know from mobile game developers, they either included ads or didn't, but never switched from one to the other. Just think, if somebody gets hooked to you game with ads, he is OK. But if he gets hooked without ads, and you add them, is he going to react negatively?.

After a quick search I was unable to find advice on the matter, but think that while people is quite tolerant to changes in large platforms like Facebook, I usually picture users of mobile games as much more volatile (after all, they have thousands of alternatives to choose from).