I've used the Surface Dial, and for what is supposed to be a dial it is not remotely what I would consider small. Small for a dinner plate, maybe. It's 2 1/3in in diameter, so it seems to be bigger than the one you linked to, which has a 2.4in base, with a knob smaller than that. It makes me wonder just how big of a "dial" you think you need. But that's irrelevant; you must suit yourself.
I suppose it's worth pointing out that your concerns about "compatibility with an app like MC" are only germane if you have JRiver's volume mode set to "internal volume".
If you are willing/able to operate it in "system volume" mode then any device that adjusts the system volume is adjusting the JRiver volume.
Google "jriver volume mode" if you are not familiar...