The electronic Omori gauge is a bit sluggish, but it's a million times faster than the stock gauge. I played around a bit with mine and found that the sluggishness comes from the gauge itself. The sensor is very fast, but the gauge seems to be filtered a bit too heavily on its input and takes a bit of time to catch up to the sensor's voltage output.
You can see this when you first turn on the ignition without starting the car - the gauge settles quite slowly to zero after doing its full sweep.