I would say making a midi controller is relatively easy.

Keybeds are a bit commodified. See http://www.fatar.com/

Making a case is low tech manufacturing.

And everything else - displays, silicon pads, circuit boards, etc - is clearly commodified.

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Relatively easy versus manufacturing anything that requires more than light manufacturing where all components can be jobbed out.

I mean we are talking single sided PCB’s with a handful of switches, pots, and encoders plus a microcontroller and display.