Tried out a new Zippo handwarmer yesterday. Followed the instructions (is that a first?) for the first burn, double filling it - in this case with Swan lighter fluid, although could just as easily use Aspen 4 or Coleman fuel I presume. (although please correct me if I'm wrong on that!) 24 hours later, this little beasty is still going strong! Without the cover, it is not too hot to hold in the hands, putting the cover on produces a lower - but still pleasant, heat.
The first "ignition" required longer than the recommended 3-5 seconds holding a naked flame to the catalyst - taking about 10 seconds before a glow could be seen and heat produced. Just pop the catalyst top back on the main body, slip the handwarmer into its pouch and off you go.