Just stumbled on to this in Apple App Store. Daughter practiced Sicilienne and Rigadoun with it tonight. Not as good as a live accompanist, but adjustable speed. It’s a screen which magnified the 10 year olds attention!
A notch better than a metronome in some ways. I play jazz and I use an app that accompanies me. I would not, however, do all my practice that way. Most of your practice needs to be very fine-control work -- intonation at super slow tempos and the like. I'm a Sassmannshaus disciple in this regard.