Midjay Plus isn't that much less than an SD-5 anyway, I thought?
My biggest gripe with these kinds of things is the whole ergonomics of it. They're really designed with MIDI accordionists, guitarists etc. in mind, but you use a module with a keyboard, and you have to get it in so close you can work the buttons while you play, you end up obscuring all the controls and display of whatever you are controlling it with!
OK if you are just using a dumb one MIDI channel out controller, but if you are using something else that makes some sound of its' own too, things can get pretty complicated...
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An arranger is just a tool. What matters is what you build with it..!