I'm a NEP fan, it is the best throttle lock that I have seen. It's cheap. With careful installation and adjustment it will hold the throttle where you set it until released, engages with a nudge from the thumb, releases immediately, and can easily be overcome by twisting the grip if need be. The only hazard created by using one that I can imagine is if the rider were to fall asleep while riding or have the right hand become inoperative while riding. In either case you will just keep on going. If you are offended by a black nylon lever next to your throttle this is not the lock for you.
I was at Bent Bike today and I just happened to see that they had Throttle Rockers. Seattle area folks know where to go, for the rest I believe that they are on line.
Steve