I have 2 of them and love them!! They stay warm for a long time, 10+ hours and then you just heat them up again. They are very durable, I've had mine for 6 years now and they still look and work great and I've used them countless times. I highly recommend them to anyone looking for a heat source for their pet.
They also have many different covers you can buy for them. I once bought a dog cover for them so that it was like laying on a stuffed animal.
Bonzo Pet Companion by Snugglesafe