I purchased the Honda OEM heated grips and sub-harness, and will install next time I have reason to remove the Tupperware.
Yes, heated grips *in general* work. The handle bar being steel is a big-time heat sink in winter. Even heated gloves are not enough (for me). And the heated grips are not enough. It's analogous to sitting by a fire in winter . . . uncomfortably warm on one side and uncomfortably cold on the other. So I need the grips to keep my palm and inside finger curl warm, and the heated gloves to deal with the wind chill on the outside of the fist.
I installed OEM heated grips on my ST1300, and they work.
I had the dealer install OEM heated grips on my '12 Suzuki V-Strom 650, and they didn't work worth a darn. The dealer replaced them with Oxford heated grips, with five settings, and those work *much* better.
I ride all year in Northern Virginia, and only twice this past winter did I turn them to position four (80%) . . . temp 25oF in the morning.
That said, I echo the other posts, that heated grips should be used in conjunction with adjustable heated gloves. Add a heated jacket liner to that, and I've never needed anything else.