My only complaint is these don't heat my grips nearly as warm as two other brands I've previously used,
Heat Demons' advertising reports them starting out in the snowmobile and off road industry. Whatever their history their thin elements are never going to bake your hands.
One thing I've noticed with them is there's a significant difference in their effectiveness depending on the grips installed over them. One bike has Kuryakyn's ISO grips. Solid rubber all the way through. The other bike has SAC grips. Even thicker than the ISO grips and a foam core.
The Heat Demons' elements are inside the handlebar. So they have to heat themselves, than the handlebar, than the grip. Once all that has been radiated through we feel it in our hands. Right side grip of course doesn't even have as firm and direct a contact surface against the bar as the left side does.
I've been on a couple bikes with skinnier grips that worked better than either of mine. On mine the bike with ISO grips performs both more quickly and with a little more warmth than does the bike with the SAC grips. Both bikes get warm. Then hands appreciated it. But the grips make a difference in overall system effectiveness.