Well then, I'm glad I got one before they're gone, assuming it works good like Bremon said. It gets toasty warm in there, trying it in the house here, but mid winter will be the test.
Good to hear. I saw it got some not so great reviews - mostly from folks that seem to think it should heat your hands instantaneously. I got it more for the same uses as your dad, and for the wife to maybe use when she comes out in the woods with me.
If he's into the line already, it's definitely a must-have. I have no other Bosch cordless stuff, but to me it's well worth the hassle of having a 2nd brand of batteries and charger.