Hello Chuck, welcome to the forum. First all three makers you mention make good stoves.
I looked at the sites for the three manufacturers. The insert from Hitzer is a hand load stove, you fill it every 12 hours or so with a bucket or a shovel. And empty the ash pan.
Hitzer makes a slightly smaller insert model 503 that has a hopper that holds a day's worth of coal, so it reduces the amount of time and attention needed by half.
The Keystoker insert is like the Hitzer you mention, it is a hand load stove.
I could not find an insert made by alaska, they have console models that will fit close to a fireplace on a hearth or fireproof surface. The Alaska stoves are stoker stoves, they burn a smaller size coal, and the stoker mechanism requires electricity to opperate. The alaska stove has a lower BTU output than the other two units, but will have a much more controlable heat output and can be turned down to be comfortable during warmer weather.
If you want a seriously heavy duty insert, the Hitzers are build like bomb-shelters. But I would go with the 503 model to get the hopper feed system, to cut down on the attention the stove needs every day.
Where are you located?? Is coal readily available?
Hope this helps. Greg L