That's a rather expensive way of obtaining broken shells to use as fire kindling

As an aside, we put all usual Christmas purchase of walnut shells onto the compost heap and I find they take ages to rot down - probably why walnut was one of those woods which was once popular for furniture making.
Did you find a source of in-shell nuts? I would have thought a friendly fruit & veg market stallholder might give you a reasonable price if you were prepared to buy in bulk. If there's an Asian fruit & veg store near you, they often sell stuff in bulk (large families). Might be worth a try.