MIDI controllers

I’m interested in discussing MIDI controllers for controlling Grasshopper and some custom robots [robot arm in my case].
I want to hear opinions from people that have used different controllers and some tips on what should be mostly taken into consideration when choosing one.

In my humble experience, I have an Arduino Uno board with a 3x3 button grid like a drum machine, with each key mapped by particular use-case and a PO-20 arcade by Teenage Engineering.
Lately, I’ve been looking into more advanced MIDI controllers, mainly ones for the music industry.
I’d like to have a synth since I like to play and experiment with music, also, they seem like very nice MIDI controllers to play around with.

I have access to a custom-built 5axis robot arm, that I’ve already gotten myself pretty familiar with through the Arduino board, but I’m seeing more possibilities with a more advanced MIDI controller.

Honestly, I might be just looking for an argument that would justify my purchase of a synth and later on, purchasing components for building my own home robot, because, from my limited experience, I have yet to find something I can’t do, that I want to, with the equipment I have at my disposal, given the setup mostly goes through grasshopper.

How are you using MIDI controllers? What are you doing with them? Why a standalone hardware component specifically, instead of driving everything through grasshopper code with CICADA as an example?
How are professionals using them?

I am looking at the OP-1 mostly. One of the best and thought-out products I’ve seen lately.
There is also the OP-Z that can do stuff with Unity, something like producing graphics and controlling animations with the OP-Z, which sounds interesting.