I had the factory heated grips installed on my 2008 R3T. They are similar in their function to the ones that I had on my FJR1300. There's a dial near the grip on the left side of the handlebar, and you turn it on or off, and dial it up, with the dial.
I kind of prefer the BMW approach where there's a simple switch with a couple of levels ... off, low, medium, high, or similar.
Even though I prefer the distinct settings to the dialed in settings, I can't complain about the Triumph grips. They do work, and I really like heated grips when the temperature drops down to the mid 40's F, and below.