I’m not suggesting you change your product. I’m simply explaining what I personally would be interested in.
That said, if you want to teach people to speak with an “American accent”, you should probably be aware that there is no “American accent”, only regional accents.
Thanks - we're aware! There's also a concept of a general American accent. Since the app is for non-native English speakers, a general American accent is the goal more so than a regional accent. We built the app together with professional accent coaches -- if you're interested in our methodology, you can learn more on boldvoice.com.
That said, if you want to teach people to speak with an “American accent”, you should probably be aware that there is no “American accent”, only regional accents.