what are the thoughts of stand alone super tweeter

Yes......

Let me throw this out for speculation/discussion.

Many reviewers and others report super tweeters to be an improvement. I have never heard speakers with them so I have no informed opinion.

They operate at frequencies we can't hear. So there shouldn't be any problem with integration with the main speaker since we can't hear them anyway.

My speculation is that they operate simply by having their frequencies interact with the frequencies that we do hear. In other words, the compression and rarefaction of air from the sound waves of the main speaker is added to or subtracted when it meets the wave of the super tweeter. So we're just altering the frequencies of the main speaker.

In other words, it's just another type of a tone control. Right? If not, then what does it do?

I'm not trolling here. I'm just trying to figure out how these things work.

Best to have one custom matched to your loudspeaker.

I tried the Onix supertweeters with 2 models of Alons. Misstl points out the possibility of coherence issues. I suspect the whitish coloration I heard in the highs was a coherence issue, super tweeters may alter the tonality of your loudspeakers.

YMMV may vary with different super tweeters and/or loudspeakers.

I have been using speakers that extend well above the audible range since the early seventies and am convinced that it is a definite benefit. BUT I think you are letting yourself in for a lot of trouble. Unless you are going to get a good electronic crossover and amplify the tweeters separately OR you are or have access to a talented crossover designer the speakers will probably sound worse. The tweeter has to be very carefully integrated with the rest of the drivers and this is the thing that separates the men from the boys in speaker design. Years ago I owned a pair of B&W P2H speakers [their first product]. This used what may still be the finest tweeter ever massed produced, the Ionic tweeter. This was marketed in different countries with different names[ theirs was the Ionafane] . It was totally massless , flat out to 30 or 40k and glowed with a blue light. It was about the neatest thing I ever saw in audio and it sounded wonderful. But even B&W did not succeed in matching it to a cone driver. If I wanted more extended highs I would change to different speakers as I think it will be cheaper and easier in the long run.