Some high end beryllium tweeters are about as good as it gets or not far off. There’s nothing bright about them, or any other tweeter that’s a bad rep, like brightness because it’s a metal dome. Be makes a good tweeter material because it’s very light and stiff, the ringing tends to decay more quickly than ali or titanium too (not compared myself, just off what I’ve seen)
Either they’re well made tweeters or they’re not, the be’s I use aren’t bright because the sensitivity is toned down in the xo. Like most need to be, soft or be. I find mostly when they’re set bright it’s intentional, to make it sound like there’s more detail and accentuate the highs. Some people like that, I find it a bit tiring after not too long
But that’s nothing to do with Harbeths so...