With the caveat that there is no right answer, I can tell you as a mobile advertising guy that your users are unlikely to desert you just because you build in s

With the caveat that there is no right answer, I can tell you as a mobile advertising guy that your users are unlikely to desert you just because you build in sponsorship. Particularly on Android they have been trained to expect ads in free products, and there are plenty of ways to do it so that it flows with the user experience. What I would recommend is that you don't let the bank completely dictate the UI - rather build in the messaging in a way that you yourself would find acceptable. Feel free to ping me if you'd like advice on the ad units.