Great in the winter
I use my FS mug on winter trips when weight and its size aren't a big concern. It's great to use inside the tent as the lid helps to keep you from spilling your ramen all over you bag and your clothes.
You can make yourself an insulating sleave or you can spend $10 and buy a neoprene sleave made specifically for it at Forty Below's site.
I can fit most Mountain House Pro-Pak or the regular two person meals inside with the lid on and they stay nice and hot while they rehydrate for 10-15 minutes.