I have used one with no kills because of it yet.
I have the Convergent App with a BT speaker and it has some great sounds. Everything from piglets squealing to boars fighting but so far nothing has ever come in to it that I know.
I do not use it every time and there have been several times I think it would have made a difference,
One morning before daylight a boar was all around me and he was mad. Grunting up a storm and moving all around in tall brush where I could not see him. If I had had the speaker in an opening I think I could have brought him in for a shot.
I will continue to use it and keep trying!