Instruct: Classify a given review as either positive or negative.
Query: Works well, not perfect

This product works reasonably well. I use it when biking to work by putting it between a glove insert and mitten. I think I've only used it 2-3 times. One problem is that if you carry the hand warmer in a backpack it might get set off by accident. If so then it's not going to be ready when you need it. However, it also does reasonably well if you just put it into your glove right after boiling- It lasts 20-30 minutes that way. I'm not sure how long it lasts when used properly but I suspect a bit longer. It does heat up very quickly (<2 minutes) when used properly.