Works well for my purpose

I use this app to practise clarinet while listening to the second voice (bassoon) from the midi file. The standard sounds are not bad, but the premium sounds are really good. Especially the clarinet sounds great.
You can import the midi file with iTunes, you can adjusts the volume levels of the different instruments and you can adjust the tempo of the music.
The user interface is not really fancy, but you can download a PDF manual.

bfd1971 about Midi Player, v3.0.2