ESBIT needs a good wind screen and it helps to only heat 12 oz. or less at a time.

The large tablets will heat one cup for instant oatmeal then a cup for a beverage.

The small tablets are good for the evening cuppa before bed.

The Vargo stove might also be acting as a heat sink to rob energy. The TI wing stove works great.

The cost and soot are both issues. I tend to use it with a 400 ml mug on fast and light solo trips.
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"In theory, theory and practice are the same. In practice, they are not."
Yogi Berra