Good USB heating pads or wraps? QFiber?

Has anybody used a QFiber wrist brace heating pad for PE?

I am looking for a heating pad that can be recharged or used via USB. This product seems OK, but I fear about it being too powerful or impossible to use for PE. Have you got any other suggestion?

I have one. It seems to give off a nice amount of heat without being too powerful. If you plan on using the battery pack, beware that 4 AA batteries will last you about 1 hour and then you will have to replace them. Last, but most important, I later realized after doing a bit of research that USB devices give off a great deal of electromagnetic radiation. That being said I no linger use mine.