I have tried them a few times. They are very convenient since you don't need a stove or fuel to heat them up but I don't think they are worth it. They have their own heating element that reacts with any liquid. One time of them heating element took about 10 minutes to start the reaction with the water and start heating up. The other 2 times i've used them the reaction started right away and was hot within 5 minutes. They are very small portions, most of them are only about 250 calories per bag. You really need two for a decent meal. To me they take up too much space for the amount of calories provided in my opinion.
A couple I had were good, and some I would rather chew on styrofoam (cheese curds). As mentioned, weight was just too much for me to pack in, and the portions were smaller.
Worked great though and the meals I had were pretty good.