User Review: Vargo Decagon
I have one of these and did a controlled test after reading the mixed reviews here. I found that 2 cups of water in a 2 QT Open Country pot was boiling the water with the fuel only half gone. This was in a 60 degree garage using my very cold well water.
I think the differences between reviewers is due to windscreen usage. Windscreens are very important for alcohol stoves. I have a homemade, full wraparound aluminum windscreen made from a piece of flashing. It leaves about a quarter to half inch gap around the entire pot and has a number of holes along the bottom. This creates the proper convection, air for combustion, gets/keeps the stove hot so the alcohol vapizes well, and directs the heat into the pot. I made it using directions on the Vargo website.