I actually still would go with the beacon. It's 433MHz signal is distinct enough to be tracked anywhere. And because an urban area may even take more search time, the beacon will last longer than comparable gps based trackers. Given the fact that at worst you basically have an educated guess on the general area where the bird landed (based on line of sight restrictions, last position recorded by the software, etc) I still like the beacon over any of the trackers I've tested...and I've got a full shelf of those in my office --everything from the gps dog collar type to the auto/vehicle type. I wouldn't bother putting those on my birds at all...too much weight and battery life is a problem with all of them.
David