This is exactly what you'd expect, a brush. Nothing fancy (except flexing the rúngne logo), nothing special, it's just a solid high quality brush.
The bristles are coarse and firm, it creates a massive cloud of chalk when brushing, it leaves the holds as grippy as new, and makes you look 10x stronger than you actually are (at least for me, 6b climber).
No suprise that it fits perfectly on the craft chalk bag, for peak climbing fashion and utility.
10/10 would buy again (if it ever were to break, which I doubt).