I installed grip heaters a couple of years back and have been very happy with them. I installed Murphs fuse block at the same time, and said fuse block now runs my grip heaters and accessory light circuits (lights now removed due to damage).
Unfortunately, I lost the high power circuit on my grip heaters a couple of months after I installed them, but thanks to my no freezing rule I'm getting by well enough with the low power circuit only. I no longer take the bike out if the temps are expected to drop below 32 degrees, thanks to a bad day with a camouflaged ice patch on an otherwise dry road... Same for impending snowstorms. The Connie doesn't take well to falls, and things generally break that you need (mirrors, footpegs, bag brackets), not to mention causing cracks and other damage the fairings... but I digress.
I installed Symtec brand grip heaters, btw.