I'm sure others can weigh in with more usage on it than my one night, but it can plainly cook low and slow for three or so hours before you need to refuel, filling the firebox as instructed. There are others who are doing a Minion-style fuse-burn, loading up the firebox with a fire brick baffle and getting ten hours.
I do love my UDS and it's set it and forget it mentality, but I could not believe the hamburger I ate last night. There's something about hot smoke, convecting without vents on top, that gave it a very different and delicious flavor. Can't wait to try ribs or brisket on it.