I started out with the Hot Hands Overgrip Heaters listed above and I liked them but DAMN did they get hot...I only had the on\off switch. If you go this route, I would definitely recommend going with a thermostat. The only problems I had with these were:
1) I wanted to take them off the bike after riding. I didn't like how easy they came off and felt better with them tucked in the bags.
2) They increased the size of the grips considerably. This would cause problems with starting the bike in gear as you couldn't get the level in far enough to catch the switch.
3) The increased grip size was not that comfortable for me. I would have hand cramping due to the increased diameter.
I now have these:
Heat Demon Grip HeatersI started out with the internal ones...they slip in the end of the bars...and I could never get them hot enough to be useful. After talking to Symtec about it several times, they sent me the under grip ones. I am much happier with them. I worked with Symtec to address a few heating issues I was having and they gave a new controller that works MUCH better (gives 100% power on high...yeah...imagine that...huh??). Overall, I am very happy with the under-grip heaters.
As for putting them on under my Kuryakyn grips...wasn't too bad. The instructions say to run the wires outside the bars but I turned the heaters around so the wires could be run around the end of the bars and in. The controller mounts so the wires are in the bars so I went ahead and ran everything inside the bars. 2 holes are better than 4 holes (Controller & Power vs. Controller, Power, Right Grip, Left Grip) The throttle side was a PITA because of getting the old throttle sleeve off. I was able to get my hands on an old one so was able to install the heater on it. (I literally tore the throttle sleeve up trying to get it off of the grip. You may want to have a spare sleeve on hand just in case...I also replaced my grips...) On the clutch side, I did tape the wires to the bar to make sure I didn't pull them off while installing the grip. Other than that...no big problems installing.
