This App makes only sense, when you connect an external MIDI device to the iPhone (e.g. iRig MIDI). “MIDI tools” is made for monitoring incoming MIDI messages (including “system exclusive” and “real time”). Some MIDI messages are visualized with bars. “MIDI tools” is for example useful to calibrate and monitor the MIDI saxophone “Synthophone” from “Softwind Instruments”.
There is also a chord and drum player function available, which allows you to easy play chords (accordion layout) or use your iPhone as drum pad. See also the integrated help function.
Please let me know if you need additional features.