It's been years (before Trunk) since I've even thought about that. The only real use IMO would be to find and auto-tune unknown freqs like while traveling or when agencies channel hopped around freqs. But keep in mind that's line of sight/close range to even work. Now with trunked systems etc, we already know the freqs. Basically, you're out and about 20-30 years ago and come upon a situation, then its of use if equipped with auto-tune to your receiver. I'm not sure if they're of any use today? Close Call on many scanners today do basically the same thing although not as efficient.
My advice is only if it's VERY cheap and you want to play around with it.
