This could be very useful for English language learners if it told you the pronunciation mistakes that you make. As it is now, it's a little disappointing. I got 98% British but I have no idea why it came to this conclusion. It could be that my British accent is good, or that my accent is rubbish but doesn't sound American, or anything else really.
It tells you which words you said it considers british and which it considered american by their red / blue colour.
It is also a binary choice. Like the hotdog/not hotdog app, you can't expect an AI to tell you much if it only has two options to chose from.