... I do find the Zippo does not get very hot and only seems to keep a pocket semi warm more disappointing than anything the older vintage ones run much hotter ...
Do you know if the Zippo you're using is the earlier one or the later one?
Are you saying that the older
Zippo model runs hotter, or that other makes (older makes) run hotter?
I'm asking because it was my understanding that the older model Zippo brand hand warmers burn quite a bit less fuel for a twelve hour fill than the newer model -- 12ml for the older model compared with 20ml for the newer model. So I would expect the older model to run cooler. I've never seen one of the older Zippo models, so I can't do a side by side test. So this is all just a theory at the moment, which I'm not very happy about because things like that have a habit of escaping and getting out of control.
I think the trick with these things is to put as much insulation between them and the outside world as you possibly can. Then they'll get nice and hot. Stuart's idea of hanging it around your neck sounds ideal if your blood circulation in the extremities is good because it will keep your whole body warm. If your problem keeping your hands warm is because of poor circulation then you might not find it very effective nor very convenient to have the device hanging around your neck. You'll want to have easy access to it, which probably means putting it in an outside pocket. In that case you might need to put some insulation in the outside of the pocket to keep the heater hotter. You'll want the pocket to close well too.