Something you've got to take into consideration is, how well does the iPad stand up to pounding day in, day out? If you are using the iPad as a control surface for the virtual arranger, be aware of just how HARD you hit buttons while you are playing. Most of us have bust a button on an arranger at one time or another, and most of those (on the MOTL and upwards, anyway) are pretty well designed pieces.
It's just real HARD, when you are playing full strength, to dial it back for a light tap on a button and straight back to pounding the keys!
Something to bear in mind...
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An arranger is just a tool. What matters is what you build with it..!