Hi Mik, the large flat blocks you have are probably the 4 gram tablets and I have been testing those. I purchased mine on ebay. I'll see if I can get a link for you 6 of them fit inside the esbitlyte burner.
Mathew is right about the weight. Mine weighs 14grams.
I received my "Esbit" brand stove yesterday and did one test this morning in my kitchen while my wife was out and about. I was able to boil 2 cups of 70 degree water under Ideal conditions in approx 6 min. and had esbit left over in the tray (I used the large cube). (see photo) After the water boiled I took the stove outside to blow out the flames. Most of you that use esbit know what a cloud of smoke that comes off the snuffed cube and what it smells like. You can see that cloud of smoke in Trail Designs demo video of the Sidewinder.
As the stove was cooling down I could see tiny droplets of chemical being given off by the remaining cube. The latent heat was enough to have the cube continue to off-gas. I was holding the stove with a hot pad and was able to get a close look of the process. As it cooled further I could see the formation of tiny pointed crystals forming at the top edge of the tray and on the esbit itself. They looked really cool glistening in the sun light. After the remaining cube had cooled I lightly, very lightly, was able to scrape the tiny crystals off and put them on a sheet to photograph them for you to see. That's a lot of crystal chemical to be handling if you are saving the remaining tablet by touching it to put it into a zip-lock bag. This is just a heads up infomercial on the use of esbit ;-) Wherever you put the remaining piece it's sure to be losing some of those tiny crystals. It would be interesting to get some input from users on how they handle their stove and remaining esbit. Eric has been using esbit for a long time so maybe he can give us some insight on how he manages his leftovers.
My recent tests with the 4 gram tablets 2 at a time in the Esbitlyte burner show no signs of the crystal formation and residue left on the pot bottom. Maybe they would form if I had blown out the fuel midway into the tests, dunno!.
In today's test we can see the amount of residue left after a 6 min. burn time.(see photo)