> It's not appropriate for a professional device since it requires you to look down and doesn't lend itself to the "mechanical" use of devices that high-paced work requires.

Sure it could; it just has to beat the cost of the lookup. If you could have done some complex operation trivially with it, that couldn’t really be done with some keyboard shortcut, being a dynamic visual field would be fine.

Of course, volume sliders don’t fit that bill, and I don’t think anyone really found something that did… but it’s not some fundamental guarantee that it would be useless.