Beryllium Tweets

Lower distortion are faster transient response, are just 2 areas where they excel

~~EXCEL~~~ you are actually describing the superior qualities of the SEAS ~~EXCEL~~Millennium~~ fast, neutral, transparent, voices human vocals with high fidelity,,where i might give the Be higher scores vs the Millennium is perhaps in the lower mid 1K-2K fq's. 
I left a  comment on that YT vid you offered  in the link,~~~JUST last night.
The guy is  talking,,,but not delivering the goods, = no actual audiotion is offered. 
Whereas you can hear the Millennium singing its magic in my uploads. 
https://www.youtube.com/watch?v=M1w_o7sZzJI

one of those people. Most ( say 90%+) of the Beryllium drivers I have heard can get bright and unpleasant to my ears

Thats what i am guessing will be my response after a  seassion with the Be midtweet.
Metal has that fault at  the highest fq;s. 
Whereas the Millennium has some special fabric, can't recall the name, which avoids these high fq's voicing with a  ~~tinnness~. And my guess is the Be will havea  bit of ~~Bark~~ in certain fq's when they peak high. 
The Millennijm has no such faults. 
There is no such ~~perfect midtweeter~~ But all in all the Millennium meets certain criterion that i wish to hear  in a  midtweet. 
With every mod in my system,,the Millennium continues to shine its true inner virtues of purity and clarity. 

Wow!  Let's all listen to the sound quality of YouTube to evaluate our components.  Besides, beryllium can and does work well with electronics that do not need the high end rolled off.  I have some, and they are great at making mediocre amps sound as horrible as the really are.  On the same system, my woven soft domes alleviate this flaw from crappy electronics.

I have some, and they are great at making mediocre amps sound as horrible as the really are. On the same system, my woven soft domes alleviate this flaw from crappy electronics.

As I said above, soft domes are more forgiving on bad electronics  /components, but not as revealing.  Beryllium/Diamond are very revealing, but you need top shelf electronics to make them sing.

Not sure if anyone on this thread invest in high end car audio along with high end home audio. If I didn’t see you at an IASCA Car Audio Sound Quality Championship (top 20 individuals), I’m sure you didn’t invest that much in that field. I won’t have the time to educate you on how some home audio products come from car audio. Example, JL Audio, Straightwire, and Focal Utopia BE to name a few. Pure Beryllium Inverted Dome Tweeter was Designed to be used in Car Audio to drown out engine noise in most Italian and German vehicles. They created massive feedback due to how the ground wire was routed and various ECU/ Computers in these vehicles. American vehicles don’t suffer the same consequences back in the day. I have been involved in high end audio for home as well as high end car audio since 1988. I’ve had the pleasure of experimenting with quite a few tweeter and crossover application. I was very fortunate to experience this. With tweeters of this magnitude, it really depends on your complete setup (amps, CD Players, preamps, speaker wires, etc). For car audio and even some home audio application, it was a bit bright for me but I did have the pleasure of utilizing the Pure Beryllium Inverted Dome Tweeter in several applications. 
https://www.focal.com/en/car-audio/car-audio-kits-solutions/elite/utopia-be/tweeters/tweeter-tbe
 https://www.focal.com/en/car-audio/car-audio-kits-solutions/elite/utopia-be

https://www.jlaudio.com/