Product review (5 stars): Keeps hands toasty warm all day long.
I've been using Jon-e handwarmers for over 15 years. The handwarmer never fails to do it's job either, and I normally get about 16 hours out of each fill-up.

Here's how it works: You take the removable main (flameless) wick top off of the handwarmer and fill the unit with fluid. Do not overfill! Place the flameless wick back on warmer and let it sit for a few minutes so that the fluid distributes itself evenly. Make sure there is no fluid on the outside of the warmer, if there is, simply wipe it off thoroughly. Light the "lighting wick" of the warmer, which is the small wick at the base of the flameless wick. Allow this wick to burn for a minute or two so that the flameless wick gets a chance to start glowing. Once the flameless wick is glowing, extinguish the lighting wick and place the top back on the warmer. Let the warmer sit upright for a few minutes to warm up before placing it in the flannel pouch. Now you are ready to keep those hands toasty warm.

It sounds like a lot of steps to use, but really it isn't. It's easy and simple, and actually takes less time to get going than the 20-30 minutes it takes for a chemical-pouch warmer to reach full operating temperature.

You have to remember that this warmer uses a glowing wick to burn fuel to create warmth, so you have to let it breathe every so often to keep it burning. This requires oxygen to keep it going, so if the warmer starts losing too much warmth, which normally will happen when it's kept in your pocket for a while, simply take the warmer out of your pocket, slide the top out of the felt pouch and set it upright in the open air for 5 or 10 minutes. This will allow the warmer to get more oxygen and start burning good again. Then all you do is pull the flannel pouch back over it and it's good to go for quite a while longer.

As for the odor it produces, it is no stronger nor any different from that of a Zippo lighter. If you overfill it and it leaks fluid then the smell will be stronger, but if used properly and not overfilled, the odor is not bad at all, and is easy to get used to. I find this type of warmer much more comforting to use than the little plastic chemical packs, because with these you can grab them tight with hands to get warm quick, without fear of them breaking, bursting, or the chemical contents leaking out all over the place. The metal housing is very sturdy and the flannel pouch is nice and soft to the touch.