Well, I installed my HotGrips yesterday. Model # 475-875.
I've had these sitting in my drawer for 2 or 3 years - just finally got around to installation as I didn't want yet another really uncomfortable late Fall / early Winter commute experience.
I love them! Rode today for the first time albeit in really nice Fall weather. They look clean (I'm OCD and routed wires, taped and zip-tied everything properly), heat up to reasonable temperatures and are generally easy to install for anyone with intermediate mechanical skills. I'm so now looking forward to the colder weather (not really - ha) now that the most significantly cold part of my body (hands) on bad days has been addressed.
The most challenging parts of the whole install are (1) routing the wires and resistor appropriately and (2) finding an appropriate power source/lead. I tapped a thick red constant +12v right after a 30amp fuse behind the battery for now. I have to go to Radio Shack or something tomorrow to get a relay as I'm worried I might one day forget to turn the thing off or worse, some idiot in the City is messing with the switch on my behalf one day lest I come out to a dead battery.
Net net, I'm very happy.
-Freddy