Our first thought when we saw this was that anyone who carries an adjustable wrench in a belt case has to be a cool guy. Our second thought: this isn’t a bad idea. The adjustable wrench is the original multi-tool and would be incredibly useful — like having a whole wrench set on your belt.
The case in the picture was custom made by a leather shop here in the Bay Area. He uses it mainly to fix bikes, though he said it also comes in handy while rigging, as he never has to climb back down for a wrench.