I also wonder if it comes down to requiring users to pay after exposing them to partial functionality (15m of recording) v.s. any functionality (must pay to ope

I also wonder if it comes down to requiring users to pay after exposing them to partial functionality (15m of recording) v.s. any functionality (must pay to open from AppStore). I think your free app is actually closer to Rogue Amoeba's approach than the pay one.