I got one a few years ago. They work, and they're fun to play with - I actually quite liked the idea of boiling to recharge - I hate nonresuable things where it costs you a buck or two just to try it out. But they are rather heavy; they contain a fluid so it's like lugging around a small hot water bottle. I wouldn't carry it camping or hiking, but it's fine to keep around the house. It's exactly the heat equivalent of those packs you keep in the freezer - good for first aid, but still kind of heavy and one-shot-use for travelling with.