Not technically "SuperTweeters" - but during the last 14 months I spent a LOT - I mean a LOT of time in the listening room tweaking gear. I was given a pair of Heil ESS air-motion tweeter/drivers many years ago. They were used in a pair of DIY main speakers mounted in (essentially) boards with two Dynaudio 8" drivers mounted both above and below them. Completely open baffle - zero crossover used - there were subwoofers in his system.
I disassembled it all when I got them and saved the tweeters. During the pandemic (having a lot of free time to tinker) I set them on top of a pair of old Boston Accoustics A40 Series 1s. Amazing. Sat them on top of some B&W 686s2's. Amazing. Sat them on top of a pair of Klipsch REF IV RF62 Tower Speakers. I've never LOOOOVED these towers, but they served well in my basement surround sound system.
Adding the Heil ESS tweets to the top - revolutionized the system. The Klipsch are powered by a MAC6700 and the ESS Tweets driven by MC250. The openness and airiness - the detail. The soundstage. I've heard amazing speakers - been in the pro audio game my entire life (I'm 50) and even though this seems like a band-aid to a marginal pair of speakers - (Head's up: It IS) - I have never heard something I love more than this setup. I'd spend tens of thousands to achieve what I've got in the basement theater.
We've been shut for a year - so I didn't believe myself. As the world opens back up, my friends have come over to listen. I asked them to sit down and listen. Don't just tell me it sounds good because they think that's what I want to hear - tell me what you REALLY think. Each and every one of them suggest it's the best setup they've ever heard (these are not audiophiles, so weight opinion as you see fit).
I recommend highly experimenting with "things" like super tweeters. Just because you can't hear above 20kHz doesn't mean a driver (and source music) being able to go way up there - doesn't still give your head, your ears and your body some "feeling" that it's there. We search for subwoofers that can extend to 20Hz and below - because you can "feel" the bass down there. I think the human body can perceive it. Headroom.
I added (I know, gasp) a JBL EQ between the output of the preamp and MC250 to tame the ESS's a bit in certain frequencies I found a touch harsh. "CUT" only - no boost anywhere in the chain.
I have to tell you, it's magical.