Welcome to the forum, that unit doesn't look like anything I have ever seen. I do have lots of experience making the triburner stoker unit work properly. If you post some pics of the mechanism I can give you some tips on making that thing work like a new unit.
One word of caution though, if it really is only 20,000 btus you will need to let us know how big your house is, how well insulated and how it is laid out. This will help in letting you know if this stove will just add extra heat to your already existing method of heat your house, or take care of most of the heating chores.
In any event, if it is dirt cheap buy it! You can't go wrong buying any coal appliance that is in servicable condition for dirt cheap.