It can get very warm very quickly
The battery lasts much longer than my old 5200mAh hand warmer.  I haven't tracked the exact run time but I have been using it on and off for two days since I received it and have yet to recharge.  I even tried the phone charging feature during the same period, which worked as advertised.  It's a bit bulkier than those 5200mAh units, so that's something to keep in mind for people who have have smaller hands.  But the size and shape fit me perfectly.
Rating: 4 stars