One thing to keep in mind is that with the Heat Demons, the element goes inside the bars allowing you to use whatever grips you like as the element heats the bars and not just the grips.
Exactly right, and IMO, that's the
problem. I've had them on my Springer for four years. It takes a long time for heat to pass through the bars, then through the grips (and gloves too) and start heating your hands. In addition, some of the heat is being siphoned away from the grips, so it's not available to warm the hands.
In the past, the Harley heated grips were unreliable, but they have gotten much better. OTOH, as OBB also said, you can use any grip, which let me have heated grips on the Springer that matched the brake, shifter, and floorboards.