A full Esbit tablet puts out too much flame under my Snow Peak Mini Solo pot. To avoid wasting heat by burning a full tab to boil a pint of water, I cut the tab in half and slip in an additional quarter to finish the job once the half starts to die down. I just save the last quarter for future use in a zip lock bag.
By the way, Esbit tablets appear to be a mixture of hexamine and 1,3,5-trioxane (see http://encyclopedia.thefreedictionary.com/1%2c3%2c5-trioxane). And hexamine itself is used as a food additive, specifically a cheese preservative (see http://encyclopedia.thefreedictionary.com/Hexamine).
Although 1,3,5-trioxane is derived from formaldehyde, and hexamine is created by mixing formaldehyde and ammonia, efficient combustion will yield primarily carbon dioxide, water, and nitrogen dioxide.