Hmm, I couldn't find anything that says it IS hexamine, but a lot of pages seem to consider them interchangable. In my search, I found the Esbit home page:

http://www.esbit.net/esbit.start.en.php

I also found unauthoritative pages that said it was harmless, and others that said it was highly toxic. Although, the one that said it was toxic was talking about hexamine, the ones that said it was safe were talking about Esbit. So if they are the same thing, someone's got some 'splaining to do. They use Esbit to power children's model steam engines, so it couldn't be too bad! The Esbit site doesn't say either way.

EDIT: I found the site for the US importer:

http://www.mpioutdoors.com/esbit.htm

This page uses the phrase "non-toxic formula - - it is completely harmless to our environment."

EDIT2: AHA! This site says Esbit is "Non-toxic"... "Much better than Triox or hexamine":

http://www.escape-co.com/stoves_and_fuel.htm