I own three of these as we lose power a few times each winter . We run them in place of our furnace and pellet stove in the house during winter and carry one during the early spring trips. They take the chill out of the trailer in no time and are very safe. mine also have a tip over protection in addition to the O2 sensor. You need to be very careful were you place them for use. In our SOB trailer, during our first usage we lit it and placed it on the stove figuring that would be a safe place for the heater. In no time at all the plastic trim around our overhead microwave began to warp from the heat. They will instantly take the chill out of a cold trailer and in my opinion, they are much more efficient than the furnace.
I will also mention that for use in the house, I have hoses that will allow me to run these from any 20 or 30 pound propane bottle. I have used them overnight and have no concerns but I try to avoid that when possible. I use two 20 pound tanks to supple propane during power outages but you can also run it off one tank by using a "T" connection feeding 2 separate lines.