I read the old posts on radar detectors and possible issues with the windshield. Unfortunately, there was a lot of guessing, and not much useful information. I recently purchased the 9500ix, and stuck it to the windshield, center of the car, just above the dashboard (bottom of the glass). It works fine, and seems to give plenty of warning. I can say for sure that the unit sees the GPS signal, the X band, K band, Ka band, and laser (since my detector has reported all of the above during the past week of driving). It is possible that the EZ-pass has some issues that require special mounting just above and to the right of the rear-view mirror (where the black dots are), but that does not seem to be necessary for the frequencies of radiation used by the radar detector. I like to test things, rather than guess. I parked some distance away from a stationary, K-band speed camera source, and then played with the position of the unit on the windshield. I can say that there is no improvement in signal strength when moving it from the center-bottom of the windshield to the "special" location to the right of the rear view mirror. What did affect the strength of the signal was proximity to the glass itself. In other words, the further away from the glass, the less strong the signal, and this affect was significant (I could go from 5 bars to 1 or 2 bars by moving it 18 inches). So the best response (earliest warning) is when the unit is parallel to the road surface, and as close to the glass as possible. I plan to do a few more tests, such as comparing the signal strength when just holding it out the window in the same convenient K-band location - in case the glass is attenuating the signal significantly, but still allowing the unit to function at an overall reduced level.
In any case, it does not seem necessary to get the $2500 custom installation on a unit designed to have the sensors mounted externally as described by a few. But if you have money to burn, why not, since the seamless installation, particularly where they integrated the lights and display into the factory mirror, were pretty darn nice. The only thing that bugs me is that the cord runs down through my beautiful 17" display, and also that if I am stopped, it will be obvious that I have a radar detector. I am thinking about getting the accessory cable for that unit that allows you to tap into switched 12V power where convenient, and enclosing the unit in something custom that looks like a GPS unit instead of a radar detector, and permanently mounting the camouflaged unit near the base of the windshield. If I take the time to do this, I'll post some pics. But for now, I thought I would post my experience so far, since I believe the information posted on this topic is way off base. Please don't respond with "I think it won't see the blah blah signal". Test it. Then report your findings.