I use them. You can put a canteen cup on a stove burner, or over a heat tab or candle, or exhaust manifold. You can shave in it. You can dig a shell scrape with it. You will die from prostate cancer (if a guy) or cancer caused by birth control pills (if a girl) long before you will get Alzheimers from a canteen cup.
By the by, with 120v capability in a lot of our new vehs, remember you can shove a bunch of rations in a 12 cup coffee carafe and pour cold water in the water side of the machine and turn the machine on without adding coffee or a filter. The boiling water will heat your rats.
Tom