Quite easy to make a measurement.
take 1 litre of water (weigh to be accurate)
repeat
Take one new heated grip and one old heated grip
Place in water and turn on
Place a thermometer in each to read temp.
At half hour intervals take reading of temperature.
Rise in temp should be noticeable in each case and if there is a difference then there will be a difference in temperature
I do have an instrument that measures VERY accurately a rise in temperature and hence measures Calorific Value of substances.
If the grips are that crap then reduce the amount of water
I'll let you do that experiment