Got 'em and tried them out on a 100 miler this AM with their dual-adjustable controller.
They do get HOT! Weird part is the hot sensation is very similar to the stinging cold sensation. Seems to be a fine line on the controller setting where you hit too cold vs. too hot. Body can trick you.
The hump in the middle (where the cable goes into) isn't as noticeable after a while. Maybe just to assure that it presses into the bottom of the foot for heat? They routed the cable in a nice location towards the inside of the boot where the zipper's at on the BMW boots. Others I saw exit the back and may be felt at the heel. Dunno.
It is easier than putting on their socks though. Heated gear takes me a lot of time to climb into and hook up. There's some cushioning too. The boot is a bit more snug as well. Overall, I think the socks are warmer overall due lack of heat on the top of the foot with the insole, and that part is pressed tighter against the top of the cold damp boot. I've used some thinner socks inside of the heated socks as the wires bugged me. Supposedly, some thinner wire socks are available someplace but I'm wondering if they are too fragile to wash?
It did get confusing using them: "Are my feet too hot or too cold?" I eventually found a null spot about 1/8 way up on the controller at which point I forgot about them being there or my feets temp. condition.
Beats nothing I guess. The convenience is they are already in the boot and not something I need to put on. I did see those chemical heat packs now for boots (much larger in size) too. Maybe get some for emergencies, but my hand ones always expire before I use them.
Oh, used the second part of the controller on a Safe-n-Warm jacket. Reminded me of using heated clothing in the Can-Bus where it turned on and off and never got hot like the old direct wired RT socket. That jacket seemed lukewarm to me over the Gerbing's I have. I realized later it was their lower wattage (60 watt) model I had on. I had it cranked full-up and it felt just warm, but not hot. My Gerbing jacket is HOT! I forget the Warm-n-Safe liners (60 watter vs. their 90 watter model) were purchased for riding two-up and not to tax a rental bike's alternator like two 90 watt liners would.