Stay away from those in a tent..
They don't contain the wax as well and if you use off brand Tea candles they tend to drift in their holders and slide to the side and can start burning more than they should and put out a lot of black carbon.
Top of my VE25 has black crap on it, surprised it didn't burn a hole in the roof while i was asleep.
Also if you bump into it by accident wax will spill out all over your sleeping bag or tent.
They are ok for if you're awake or sitting it on a table.
The original UCO is the best, they contain the candle by pushing it up with a spring keeping the wax residue to a minimum and well contained if you bump it.
I have never in 30+ years had any issues with fire mishaps other than dropping them and breaking the globe.