The heat doesn't seem to be an issue. I replaced a 35w bulb with a 20w LED. It does get warm to the touch, but not hot. I have no problem keeping my hand on the headlight lens. I checked it after riding home from work, about a 15-20 minute ride. The old bulb was definitely warmer. The heat filters around the inside -of the headlight, just like the old incandescent. I think little fan on the end of the headlight distributes the heat fairly evenly in there.
I think heat might have been an issue if I had gone the other way, say using a 50w halogen H4 to replace the 35W HS2.
The safety improvement is excellent. I can see at least twice as far down the road as I could with the old light. In dawn/dusk lighting where I could not see a light there is now a bright spot on the road. I mentioned before that at 30mph I could not see the place I was going to be in a second. I was going faster than my headlight would shine for safe riding. That is not an issue now.
