One of the most important features of a good radar detector is the ability to react to instant on radar detection.
Many of the radar guns used in traffic enforcement today, enable the officer to have his radar gun in standby mode until he has a suspected violator within range. At this time, he switches to active mode and is able to capture the target vehicle's speed.
By having a good radar detector that has long range, you would be able to pick up an officers instant on radar gun ahead as he targets other vehicles.
Also a good radar detector that reacts well to instant on, may give you enough time to react before the officer has a chance to actually "lock on" to your speed.
The following is the Instant on results from the 2003 Speed Measurement Laboratories testing:
