Good luck. The "lag" time would only add to the existing "lag" time it takes the detector to pick up and register the radar signal. I am a cop and don't really write a lot of tickets but I love to tease the drivers with visible detectors when stopped near them in traffic. I purposely turn the radar on and off when I am right next to them to see how long they will pretend to ignore it because they know I'm there (I am amused by little stupid things like that). When I do this I am always amazed by the delay between my turning it on and the detector going off - as much as 3-4 seconds sometimes, plenty of time for an officer to get a good reading of speed. Actually, the sudden drop off of speed can be used as further evidence of speeding later.
I will grant that the detector will alert to radar being used on another driver and possibly you will slow down, but when not in traffic the cops gets your speed well before your detector goes off. Oh and I always write the ticket for speeding when a detector is visible.
$300? I prefer to just not speed excessively. Easy to not get tickets that way and most of the time when someone goes flying past me and we happen to be going to the same place I usually pull up right behind them at the red light...so what's the point?
Does Escort make this type of device? I have never had a detector in my windshield and never will.
I also believe cobra is one of the lower end detectors. Escort doesn't have an iPhone one but I wouldn't want it to be wired thru the phone due to lag. They do have a mountable version that you can mount behind the grill and wire it into the cabin. It won't be a "visible" detector unless you know what to look for