"We just called them "Heat Tabs" and to be honest I only used them a couple of times."
Trioxane heat tabs are OK, but not great. In Korea, we had to use those in a foxhole to heat up coffee. If we didn't use Trioxane, we had to pry the back off a Claymore mine and pick a piece of C4 explosive out. It would burn about the same, but you just needed to be careful how you handled it (not recommended). In general, Trioxane heat tabs are much larger than Esbit cubes, so you were supposed to break the bar into thirds.
I have a box here:
FUEL, COMPRESSED, TRIOXANE
Chemical Compounding Corp., Riverhead, N.Y. 11901
Three bars in one box for $1.