This app does have ads, but as far as I can tell they only play once you have finished a session of counting (I finish after feeling 10 kicks).
The best part of the app is how it shows the data. I can see how long a session is taking, how much time has elapsed between recorded kicks, and a bar graph shows the data distributed into 4-hour increments (so its easy to see the times of day when baby is most active). This is more info than you get with built-in trackers, e.g., the Baby Center app, which is a poorly executed kick counter.