Can anybody give us a shred of useful information?Can anybody
As always, you've overly critical, while not 'HiFi' they have been used in millions of PA and instrument cabinets over the decades, and perform perfectly acceptably in that role. In fact no doubt you have many recordings that feature such devices, you wouldn't know, as you can't tell.An audio power amplifier that can drive a 4 ohm load can drive 15 paralleled piezo tweeters up to 20kHz.
Piezo tweeters were used 50 years ago. I am surprized that they are still being sold as replacements. I found them at Parts Express at a very low price but with absolutely no audio spec's. Reviews say, "Not for hifi".