I've never heard of Datrex and can't comment about it (them?) directly, but I can say that 150 calories per ounce would be a pretty decent calorie density for something that resembled food, rather than resembling a stick of butter.

If you are just out for convenience, then food-bar types of things are pretty convenient. You unwrap them, chew and swallow, and your work is done! But if you prefer to put in a bit of work and thought regarding food, you can eat real food, get a similar calorie density, spend less, and have more variety.