I've been driving with my XRS-9300 since december now. Its saved me a number of times now. I think some people misunderstand the use of the cobra.
Its cheap and it has alot of false alarms. My friends are annoyed to death by the constant X band false alarms that I don't even hear anymore. But when a K or Ka comes up I have enough time (barely) to slow down to the speed limit.
Cobra's do what they're intended to, just dont expect them to do anything more or even that well.