Just to clarify...
The Mr. Heater is not a Coleman product. Coleman makes the "Black Cat" catalytic heaters in a couple different sizes. I have a smaller one and it works for very small spaces but you need to be in front of it. I also use the Mr. Heater which comes in various sizes and accomadates various sized propane containers. I have the small one that is approved for indoor use and runs on a 1 lb propane bottle. I bought a high pressure hose for it and run it of a pancake shaped 4# propane cylinder in my small trailer. It is designed, as chimmer said, to shut off if knocked over or if the oxygen sensor is deprived. I believe it requires a minimum 6x6 opening for ventilation. It gets nice and hot when using it. I also have the bigger Mr Heater which mounts on a big cylinder. That kicks out serious "patio" heat and you can even cook on it if you lay it down. It CANNOT be run in a confined area.
Mr Heater
Similar to my larger Mr. Heater