Never had em, talked with a few fellers in the service what had em. Will keep ya alive but yer belly still gonna growl. I like the survival bars better, ya still gettin calories an other stuff, but there be something goin in yer belly to.
They say you can use the container as a canteen and they even have a bag in there to transfer the tabs if need be. They're not bad tasting, a neat snack, but you'll need some water afterwards. I first saw them back in the early 1970's, I believe, we got some in the sort of container that you get bulk spices in now. They were sold as some sort of modern, high tech, astronaut type food item for active children.
I stockpile a wide range of things and I keep a few of the containers around and I do rotate them.