I had one in my last truck and loved it. I used it for both winter(heat) and summer(A/C) I've yet to get one installed in my current truck. My advice is shop around. Ask around about reputable installers in your area. Most shops will stand behind their installs. I paid about $300 for the system on my last truck. So, $400 isn't that far off considering the ignition you have in your car.

A note on warranties...You cannot be denied coverage by simply having an aftermarket part in your vehicle. If anything goes wrong they MUST be able prove that the aftermarket part caused the problem.
http://www.semasan.com/main/main.aspx?id=60128
Magnuson-Moss Warranty Act