Esbit tabs produce a lot of heat for around 10-14 minutes. They're great insofar as they're shelf-stable, easy to use, and can be used to boil water or start a fire. They also smell bad when they burn.

Sterno produce less heat in the same amount of time but burn for more like two hours. They don't smell bad. Much better for heating a small area to keep warm. Sterno doesn't emit carbon monoxide, so that also makes them safer. Don't try to boil water with it though.