The biggest factor that the police Charger has against it is the price. I don't know the figures off the top of my head, but the Chargers are at least a few thousand more than the standard Crown Vic - maybe a little less for the Chevy Impala, but right now, the Charger is by far the priciest - and that's a tough pill to swallow for some municipalities.
The Charger is the first true police competitor to the standard Crown Vic since the Caprice went away after 1996. There are many that have come along since then, most notably the Chevy Lumina (later Impala) and the Dodge Intrepid (and in some cases the Ford Taurus). But cops as a whole despised all of them. Most cops I know can't stand the current Impala for the same reason - they just don't have the room that the cops desire (and need). Especially today with all the computers, firearms, body armor and gun belts - they require alot of room, and the Crown Vics are the only ones that truly have that kind of room, which is why, along with the cheap price, they still remain a police favorite.
But I do think it's cool that Dodge is finally being taken seriously again in the police market... except when there's one looming in my rear view mirror.