I have a Lieca rangefinder, and learned the hard way to keep it around my neck when bowhunting. I wouldn't have even attempted some of the longer shots I have taken at antelope without it. And even when using it, you range the animal - or a spot on the ground near the animal - and then, by the time you get an arrow nocked and drawn back, the 'lope has sometimes moved a little. But you're right - the rangefinder somewhat minimizes the need for light fast arrows. I wonder how many 3D shooters would use the real light shafts if rangefinders were allowed in this sport?