Kief is fine directly in the trench. When I'm in a "kill the pain/get fucked up" mood I'll load 3/4 of a trench of just kief. It might be a bit harsher on your throat and cause you to cough more, but I suspect it has something to do with THC's known bronchiodilator (opens up the airways) and expectorant (makes you cough) properties. I like hitting it 3-4 times dry, and then hooking it up with some water path. Hash and other "purer" concentrates will gum up the screen, but you've got a lifetime warranty. Bubble hash, in my experience, does well mixed with a pinch or two of herb.