Here is a youtube video of the microTach+ Tachometer in action. Please note that when reving a motor without a load (ie. Neutral) the RPM jump around ALOT more than they would on the Road. But from the video you can see that the Update rate is very fast, and there is no lag.
http://www.youtube.com/watch?v=4AeUrJGRGHk
Thanks and Ride Safe,
Justin