I’ve had Oxford Hot Grips and Symtec Heat Demon grip heaters. The old style Oxfords were good, the last set rubbish and the controller broke; overall I preferred the Symtech pads that go under normal grips.
Symtec Heat Demon

I have now seen the light however, use heated gloves, and probably won’t go back to heated grips again. Gloves heat your hands quicker and more efficiently as the heat doesn’t have to work its way through the grip rubber and glove. I also never found that heated grips kept my thumbs warm – gloves do. One big advantage with heated gloves is you don’t have to remove them, or sell them with your bike! If you’ve got more than one bike gloves make huge economic sense too.
Keis heated inners start at about the same money as heated grips.
Keis Heated Inners
Keis gloves are around �100 and Gerbings a little more, but well worth it in the long run. I use
Gerbing T5