IME, they don't work well. The good news is that I don't think they're necessary. Here is the trick:
1. Crack open the driver's side window 1-2" and leave all other windows and the sunroof closed.
2. Set your HVAC system so that it is bringing in fresh air (not recirculating) and so that all of the vents are open and aimed towards the driver's window. Use the setting that splits the airflow between the panel vents and the floor.
3. Turn the fan on full force and leave it that way, and use the thermostat to control the temperature.
4. Hold your cigar in your left hand, and be sure to keep rotating it periodically, since the airflow will mess with the burn.
That's about it. You may have to fiddle with the exact positions of the vents and window, but your car should stay odor-free. This system works better, the faster you go, so if you are in stop-and-go city traffic most of the time, it might not work for you. Be sure to empty the ashtray as soon as you stop --- ashes hold, and release, a LOT of smell. Once in a while, you may want to spray Febreze, but my wife can never tell when I have been smoking in my car. :thumbsup: