My GrandAm has this built in. I never touch the head light switch at all. DRL during the day, and when it gets dark enough out the headlights come on full. Only annoying part is that its impossible to turn the head lights off at night while the car is running. The GA also has a timer to kill the lights after about 30 seconds of getting out of the car.
If you can get it to work, it's an awesome feature to have. Just don't drive another car without it and forget to turn them off