That's a nice piece. And small too!
Personally, unless you're going to mount it in the exact same location as stock(?) I would just get two and wire one up with constant power from the Black w/yellow, and wire the other up with switched from the Black w/green wire.
They're so inexpensive, it might be worth trying to get the two to fit and play nice together in the limited space that Broncos always have.
There is a third circuit of course, which is the smallest fuse in the stock panel, for the instrument illumination lamps. Blue w/red stripe wire that is hot only when the headlight switch is in either of it's ON positions.
Haven't looked at it really closely yet, so can't comment on the "grounding" aspects. If re-using stock wiring, there is no need for a ground wire to the fuse panel.
The individual components are grounded at various points on the vehicle. The panel itself is not in need of a ground. You simply have Power-In on one side of the fuse, and Power-Out on the other. No ground, except for potential new circuits where you can run the ground right up to the fuse panel for a common area.
That's the most common scenario anyway. I'll have to have a closer look at the one you linked to.
Paul