I've got one installed on my Uniden BCT15, and it's about the third of its type I've had in various vehicles over the last few years. An external magmount works better... even a thru-the-glass works better. The attenuation (loss) is pretty severe. It also has some effect on the AM/FM radio reception (loss). Effectively, a major compromise. I have a direct comparison all the time because I have an Alinco DR-635T scanning some of the same channels, and it has an external Comet antenna mounted rooftop. The Alinco often hears things the BCT15 does not. BUT, you've got to ask yourself how far out do you want to hear things in your mobile? My primary interest is in car-to-car transmissions within a mile or two of my vehicle. This antenna handles that. And for high power sigs such as county fire dispatchers and repeater sites, it works fine. With the added advantage that it does not require adding any antenna to your vehicle, it may make sense for you. But it is a sub-par performer on both your scanner and your AM/FM radio. If there is some way you can get a separate scanner antenna outside the vehicle... or even a thru-the-glass antenna... go for it.
