Really live up to their name.
How long they will last of course is dependent on various factors, like ambient temperature and draughts,etc. But my experience with them has been excellent and while I've haven't timed them, they do seem to last forever. Wouldn't recommend for a cold environment however as they can burn out out before all the wax has melted. This is true of all candles however, depending on the wax used and the quality of the wick.