I just began using the iPad app "Set List Maker" with additional midi feature. You can also combine it with another app called "iMidiPatchbay". You just need one of the midi-usb interfaces for ipad (I have iconnectmidi2+).
With these apps you can control several instruments simultaneously and send sound change messages. E.g. Roland sound modules like SonicCell or Integra have the problem to just have 64 storage locations for sound combinations (performances/ studio sets). You get rid of these limitations by using these apps. You can also split kayboards into several midi key zones by the app even if the keyboard itself doesn't have a split function.
These kinds of apps are preferredly released for the iPad, not as much for Android tablets.