I just got an Ergodox-EZ (ergonomic split keyboard which takes some adapting to), and their helpful training tool [0] leverages WebUSB (which I didn't even know about before I started using it). It's useful because it can talk to the keyboard to find out what's the current layout and layer, and show you the relevant info and keys being pressed.
From my point of view as a user: on one hand it kind of sucks because I use Firefox as my main browser, and launching Chrome/Chromium every time is a bit out of my usual path.
On the other hand, I appreciate not having to install something on my computer just for this. It's nice for small apps that you won't be interacting with that often or for too long.