This morning was a perfect example of the need for both.
Left the house at 55? wearing my summer (half mesh) gloves. Probably shoudl have gotten the full leather gloves out, but didn't, felt fine. After 25 miles on the highway and getting into the river valley it started to take it's toll, fingers were getting sore as they were getting cold. Put the grip heater on a low setting, got the blood flowing, felt fine. 20 minutes later, off the highay and at the slower speed didn't need the heater. Going home tonight in the 70?s I will like the mesh gloves and not need the heater. But the grip heater is there at the ready.