Anybody use one of these?

Would it be totally insane to stick it into the bottom of the sleeping bag during the night?

No, perfectly safe but you'll have to carry the weight of it around (plus fuel)

Just looked at a demo on you tube, it's big, almost as big as an adults hand. Placing it in the groin area over a femural artery would help warm the whole body by heating your blood up.

I just use a water bottle (or more normally a small nalgene) full of hot water, wrapped in a sock. Boil a bit extra with the pre-bed cuppa and you've got a hot water bottle.

^^ this

Its a good way of keeping warm and/or warming your bag, plus you've got some unfrozen water to use in the morning

Of course, one way of filling the bottle with "warm water" means you don't have to get out your sleeping bag til morning!

That was an actual bona fide tip I read years ago. It didn't say if you should use a special bottle for it!

A guilty secret of mine has always been the old 'oh naturel' hot water bottle trick. Only to be used in times of extreme desperation.

I havea Whitby handwarmer that it's I think the same as the Zippo, it's great and doesn't weigh much at all. be aware that they can be a bit of a faff to light without the bit of fuel to squirt on the bit you light. theyalso take a few goes to reach max running time, last time I used mine it ran for 12 hours. I also wouldn't use it in without a bit of ventilation as it must give off c02.

I think I'll go with my daughter's small hot water bottle. It's pretty light and won't take much water to fill it to keep the toes toasty :D