Its one of the first things I install on everyone of my sleds for about the last 15 years. I work with my hands all day, everyday and my hands will start to cramp up if I ride a sled all day without a lefty. I bet I use the left hand throttle about 30% of the time just to rest my right hand.
Anyway.... They are super easy to install. The only tips are getting the through bolt on the flipper installed correctly with the washers, and dont over tighten it. Also make sure the throttle cable in adjusted correctly. I ALWAYS leave the throttle safety switch functional, just adjust the cables right and you wont have any problems. Dont worry about the Lefty being able to get the sled all the way WOT, you almost never need that when your using the Lefty.
oh yeah, you may have to move your left side controls in on the bars to get enough room. I clamp the throttle to the bar, not over the grip. I also use the clear rubber sleeve (I think they send this with it) over the bar, then clamp on the lefty. You should end up with a gap in the rubber sleeve, thats where I run the wiring for the heated grip through.