Iguidance does lag about 1 1/2 seconds behind. I'm a truck driver and use it just about every day. Theres just enough lag time that can screw you up in some situations. For example, if you take a off-ramp which curves and splits at the end of the curve, you can take a wrong turn if for some reason you didn't hear the voice prompt on which side to take. Which has happened to me due to someone yelling into their CB or I'm jamming to some tunes...