They haven't been made in 30+ years, and unlike most older sirens, several East coast fire departments still run them. They seem to have a cult following because of the distinctive tones, mainly "warble". Many "oddball" (off-brand) sirens were Federal Signal clones, or just didn't sound very good, but the Powercall was unlike anything else.
I ran a Powercall in an unmarked detective car until 2001. EVERYBODY knew who was coming! And people moved out of my way. Best siren I ever used, new or old. The deeper tones penetrated car interiors better. Most newer sirens sound weak and 'tinny" in my opinion. They don't have the punch of the older sirens.