I've used Cowboy brand for a few years now. All your input makes me wan to change to something else, but not Kingsford briquettes. I have found a few smallish rocks in my bags which burned me up. The shake at the bottom of the bag is mostly a waste. it will eventually burn, and burn hot and long, but it will take a good long time (hour plus) to get the fire burning right.
I do like the big chunks, I can throw a few on the fire and run up to the pub for a pint or two, when I come back the fire is still burning good and hot. Mostly what I've found is that you need to run a few bags, sort the chunks by size as you pull them out of the bags, sort like sized chunks in bag with similar sized other pieces. Mixing the shake at the bottom of the bag with medium size pieces, works well, small pieces when you need to make a small temp adjustment and larger pieces when you need a pub run.