I've been running a Warm Morning 520 on salvaged stoker size high volatile Illinois soft coal for a couple years now. Everyone says this is a great stove and I agree.
But it is a bit tricky to get it to run the way it was designed. Those channels in the firebrick are there so that it will side/down draft, and thus burn all or at least most of the smoke and volatiles. Once you get it drafting through the channels, and not up through the fresh coal, most problems with smoke or run away high temperatures will disappear.
I start the stove like everyone else on wood, and start adding shovel fulls of coal as soon as it gets going good. I throw it against the back wall. I keep adding coal every 5 minutes or so, being careful to keep the front hot and with a decent flame. It does take time. Over the course of an hour or so I might load it up with 30 to 40 pounds. But it is always controllable using the MPD and primary air.
All this gets us a fairly deep bed of burning coal, but it's still drafting up through the top, not the sides. At this point I fill up the stove with another 50 pounds of coal or so. This in effect closes off the top and forces the stove to now draft through the firebrick channels. This creates that wonderful 3 zone effect of the coal on top being coked with the gases being drawn over the hot coals and burned.
With the coal I use, when I get it wrong, it becomes a smoking mess. I've had neighbors a quarter mile away complain. When done right you can't tell that I'm burning anything.
Great stove. I have burned a lot of junk coal and it just keeps going.