I've used one in the past. On the non-800 public safety bands, with a BC200xlt, it worked better than the stock rubber duck. A dedicated external antenna gave slightly better reception.
I have used for years and it works, including 800 mhz. The down side is many scanners put out a pulse as the scan and you hear it in your car radio. Some scanners were so bad could only listen to radio or scanner, not both.