I've had both the Hot Foot and currently the Hotronic
boot heaters. I noticed Hotronic has a newer battery with a longer life than the model I have. I had the first generation of the Hot Foot. The batteries were awful. I'm sure they're better now. I didn't like how the batteries attached to the boot. I used to see lots of batteries at the chair loading ramp.
I ski all day in New Hampshire and get cold toes easily without the heaters. Call me what you will, but I love my warm toes. The newer hot foot model with the thermostat looks inviting. You have to be careful not to overheat your feet. They will sweat and get colder faster.