Very cool Steve. I'd been using charcoal pencils in much the same way, except I only had black
The stuff works great folks, lots of control and it wipes right off, no sweat at all if you screw up.
The charcoal, as I imagine the chalk does, works great for weathering anything. Gloves? no problem! Boots? same deal. If you need to weather anything that's cloth these will work great because you can just rub it in and, don't quote me here
, it likely washes out too!
I wonder how it would look on trooper armor? It's gloss finished so I don't know. But I might just find out 
Thanks Steve!
Phil