Once upon a time I did a lot of CAD/CAM and used an external control board for visuals like rotating and zooming (good ol’ Silicone Graphics days). Once you get used to it, the speed boost is amazing. I do a lot of repeated tasks for 300ish images and it takes time to fling around with the mouse. A panel like the one above, shortcutting things like exposure, tone eq, sigmoid etc…
Then do as darix indicated and search the forum for loupdeck and MIDI. As far as I remember the latest with substance on this topic has been the loupdeck settings from @hannoschwalm.
Well, you might have a look at the Behringer X-touch mini, which works out of the box with darktable (at least under OpenSuse Tumbleweed). You just have to set up the short-cuts
This kickstarter thing starts at $300 USD and goes up to almost $1000 USD… and its a kickstarter so they don’t even have to actually give you the hardware…