After living with each unit successively for several weeks, I spent one day running errands with both mounted to my windshield in an attempt to see which had the best balance of sensitivity to legitimate threats combined with a reluctance to cry wolf while cruising past static door-opening radar devices that constitute the most common form of false alarm.
The Passport won the sensitivity contest by a small margin with an earlier warning on multiple occasions. It also proved the least likely to sound off when no legitimate threat existed.
One highly endearing Passport feature is the ability to mark and hold in memory those annoying false alarms you encounter on your daily commute. The GPS location and signal frequency are stored to block warnings that only distract. Speed traps, cameras, and other threats can be marked to provide a useful reminder when you travel through perilous enforcement areas.
The less expensive Cobra is the detector for the gadget afflicted. It not only receives a claimed 15 bands (though only 13 distinct radar and laser frequencies are listed in the manual), it also displays a compass reading and battery voltage in its color monitor screen. Like the Passport, it is possible to store locations in memory - up to 1000 of them according to the instruction manual - but that requires sifting through a 40+page booklet printed in type small enough to glaze the eyes of a monk. I was surprised to notice that many known stop-light camera locations are already in memory and available for automatic protection.
Bottom line: The Passport provided excellent warning, good resistance to false alarms, and easy plug and play operation. The Cobra probably has equivalent performance but dialing it in to suit your preferences requires negotiating several operating menus.