If you're concerned about the heat, you can always place a thin sheet or towel in between your skin and the heater! Like most small electronics, there is a small chance of overheating! Just use common sense and don't keep it runnin' overnight or anything like that! It comes with two power cords, one that plugs into a regular wall and another that plugs into your car, making it easy to use on your commutes, too.
Promising review: "I purchased my first Zyllion on 5/24/2014. My little friend died tonight, 10/13/2018. This wonderful little gadget came to my aid multiple times a day, and never complained. I sat on it, dropped it, lay across it — virtually lived on that thing. It's been my go-to pal when I was sore from surgery, from work, from a long day in the yard. I have severe arthritis, bursitis, plantar fasciitis, frozen shoulder, joint pain, tight calves, and a replaced hip and shoulder. This modest little piece of equipment is phenomenal for loosening tight muscles and relieving pain. These guys are top notch, reliable little beasts." —white noise machine
Get it on Amazon for $44.95.