So I ordered one of these during the summer for a bit over $20 and I've been really happy with it so far.
I was looking for something that would be good work because I work outside year round, for camping in late summer, snow boarding, going to school in winter and whenever else I get cold hands.
There are a lot of pros and a couple issues.
The good is that it gets really hot fairly quickly (once it's lit), is pretty efficient on the fuel, it's re-usable, it's light, and it is the perfect size to fit in your hands/pocket whatever.
I filled it with about 3/4 of the capacity going off the little filling thing that comes with the hand warmer before we went to bed and it was still warm when we woke up.
The issue that I have is that it can be a bitch to light initially. I've sat there for a few minutes trying to get it to light and sometimes it just does not want to light up.
The other bad thing is that the little case that comes with it muffles too much of the heat for my liking. When you do take it out of the case it can be way too hot to actually hold. I tend to just keep it in my pocket without the case and just not touch it and it works okay.
I love this thing and I can't wait to use it for snowboarding this winter and I would recommend it to any one looking for something similar.