Works ok when plugged in.  Definitely not "rechargeable" though.
These work ok.  They put out a decent amount of heat, but not so much as to be uncomfortably hot, which is important since there is no way to adjust the heat setting (aside from unplugging them).  Together the pair consumes ~8.5 watts of power total at 5 volts.  (See the photo of the USB power meter that I uploaded.)<br /><br />I also uploaded a photo from a thermal camera showing exactly where the heating element is within the insole.  The heat is produced in a thin band/loop and is not as evenly distributed as the seller's photos imply. But in practice you can't really tell just how localized the heat is -- it feels more spread-out when it's worn inside a shoe.<br /><br />Lastly, I don't know why the seller calls them "rechargeable", as it's a completely untrue/misleading label (although this seems to be a common claim among sellers of similar heated insoles on Amazon, no matter how untrue).  They have to be plugged into a USB port to produce heat, and after they're unplugged the heat doesn't last for any significant amount of time.  So if you want to use these while on-the-go and not be tethered to a wall power adapter, a simple approach is to have a USB battery power bank in your pocket and then run the wires up your pant legs to plug into the power bank.  Voila.
Rating: 3 stars