A bit of an update. I've just tested the fuel side by side with zip fuel in a Crusader ONE (Original) burner and mug. Please bear in mind that the Crusader TWO is designed to burn the Firedragon fuel. (Hence the taller burner with more channelled air flow). The tests were conducted with 0.5l of ordinary cold tap water, inside an outdoor shed (so perfect conditions) at 14c.
The FD fuel is a transparent solid gel like substance which smells like alcohol gel. The plastic and foil pot it is supplied in needs to be disposed of separately. There are only 6 cubes to a pack.
The fuel lit very easily and burned well immediately and very cleanly, in fact the only marks to the (clean) mug were signs of heat discolouration. The covered mug came to a rolling boil at 5mins 56secs, with the usable flame dying off at 6mins 30secs and extinguished at 7mins 15secs. There was a small amount of a black hardened substance (imagine burned sugar) which was scraped off. A rub over with a wet cloth returned the mug and cooker to it's original state.
The Zip fuel is lit through the plastic covering, so nothing to carry out. Lighting was not as easy but not difficult. The fuel smells of coconut slightly. The flame was very yellow and produced LOTS of black smoke. A rolling boil came at 9mins 2secs, but burned on to 14mins 30secs before extinguishing at 15mins 20secs. There was a small cube of burnt fuel left and when removed there was a small bit of unburnt fuel beneath that. The mug was absolutely caked in soot. 5-10 mins later with washing up liquid and a nylon pad returned both mug and cooker to a near original state.
Verdict?
FD- Clean, fast but does not last long. Not many cubes to a pack. May not be an ideal choice for purification by boiling.
Zip- Long lasting, more plentiful per pack but makes a hell of a mess. I would NOT want to drink out of the mug without cleaning it and the water smelled of the fuel slightly
My choice to use with the Crusader? Fireside embers or meths/methanol.