Hi Satellite mummy,
What brand did you see?? Not all brands are effective.
Currently I'm using the Tiger brand food jar. It only has one compartment. It comes in 0.7L and 0.9L. I bought the 0.7L. I use it to bring porridge for my son's infant care. I pack the porridge at 7am and my son eats it at 11am at the infant care. It's still piping hot when my son eats it at 11am. Usually before I pack the porridge I will fill it with hot water first to "warm up" the jar. After that I'll pour away the hot water, then put in the porridge.
If you can wait for Taka sale, they offer 0.9L Tiger food jar + 1 free Tiger thermos for hot water. That thermos is very good too. I'm using the 500ml version. It keeps water very hot even after 8hrs, provided your flask is almost full.