They work okay but I will tell you that when I lived in Missouri me and some buds went deer hunting for the last few days of the season. So mid January. We decided to tent camp.
Long story ahort....buddy heater worked well until the temps dropped and the tank froze.
I've had that issue as well, thats why my tank gets wrapped in a old wool horse blanket and it will keep your tank from freezing over. Also depending on your size of tank you could bring it inside where you are warming up.
Otherwise I use my buddy heater to take off the chill too, and not all night. But I do leave a window cracked open so there is some fresh air and this also helps with condensation. I set the heater on a collapsible metal table under my tents ladder and it heats both the annex and the upper tent almost uncomfortably hot. We used to use the little propane bottles, but we found it more economical to use the 5 lb tank for both heating and cooking. So we purchased the Mr buddy heater hose.