I have had the opportunity to use the Zippo Hand Warmers. Let me tell you, these things work marvelously! Very compact at about 4" x 5", they fit easily into a pocket of any shirt, or jacket.
To start it heating is a simple matter of filling it with lighter fluid, then capping it, and heating the element for a couple minutes. Once heated, there is no flame, but if you let it sit inside it''s case for a couple minutes you will feel it heat up.
Since there is no flame, it is safe to put in a pocket. I have found when fishing that after I hook and reel in my fish, that my hands are wet and cold. This product is very efficient at warming my hands up after I dry them off! I can also see where I will be using it in the lower back pocket of my shirts to keep my lower back from tightening up in the winter out in the snow and ice.
It's cost is less than a good pair of gloves, and I can honestly say that I don''t know how it couldn't be called a necessity for me and my business! Simply put, this unit functions well and does the job when I need portable, compact heat anywhere and anytime that I need it.