If anybody says they won't light in sub freezing cold don't believe them! I've run mine at -30C. You will need much more fuel however. Priming them in the cold can use a lot off fuel and you'll need longer burn times to boil water.

If you have winter/cold weather in mind, make sure your pot/cup as a lid and get a good windscreen that covers the entire cup so wind can't blow past and steal your heat...and bring more fuel than you think you'll need.