While your thoughts on fuel burning are probably true, the only way to know for sure it's burning more fuel per boil is to weigh the fuel canisters before and after. I picked one of these up on the sale and was playing around with it a bit today. Not a very controlled test as I used two different canisters I already had laying around but I compared it to my Optimus Crux Lite stove and Olicamp pot for burn times tonight. The Olicamp pot is a wider (more surface area closer to the heat source) 1 liter pot but I only filled it with 0.5 liters to match the Primus. Indoor conditions side by side my Optimus boiled the water in 1:55 while the Primus boiled right at 3:00. That said, I could hear the difference in the output and wouldn't normally run the Optimus at full bore like that. That thing was burning alot of fuel fast. It certainly boiled the water faster, but I think it was also burning more fuel per second as well. If I had backed it off a little it wouldn't have boiled so fast but might have been more comparable to the fuel burned per second of the Primus. Again, I didn't weigh anything before and after to know for sure, but I could hear a difference in output enough to make me think faster boil times alone don't necessarily mean more fuel efficient.
