My OB heat to feet appears to work well. I keep it on combined feet/defrost setting.
It's been 0-15F depending on the time of day lately. I usually do not preheat the car for longer than it takes the high idle to lower, and I'm off. Have 2.5 miles of dirt road at max 25 mph before the car gets above like 2300 rpm except on the rolling hills maybe up to 3k rpm. By the time I hit asphalt the blue light is off.
I wonder if this issue is tied at all to attire? I wear an insulated leather boot all the time. However, I see people wearing CROC's year round. I know when I wear my Johnston & Murphy's with leather soles my feet get cold in winter.