It's OK for a brew in warm conditions - I wouldn't like to use it as a main cooking fuel though. It's also good as a fairly bombproof means of starting a fire in a hurry.
I haven't tried using in in the cold, but if I did, I think I'd try to warm it first and insulate the cooker from the ground. Like I say, I haven't tried it, so I don't know if that would really help much.