MIDI controllers control MIDI devices. They do not make sound no matter how high the volume is set.
One of the main requirements for having an app distributed through the App Store is that the app should work as described. So one star reviews claiming “it does not work” should be ignored.
If you have a Mac you have everything you need:
- Launch your MIDI app (in this case Pad MIDI on an iPod Touch)
- Launch the Audio MIDI Setup utility (found in the Utilities folder within the Applications folder)
- If you are seeing the Audio window select Show MIDI Window from the Window menu
- Double click the Network button to show the MIDI Network Setup Window
- Join a Session by connecting your device
- Launch GarageBand which will find all MIDI connections
- Play the app to play Garageband