Beryllium Tweeters - Your Opinions & Comments ??

Audio from properly implemented Be speakers is anything but  "metallic" and bright.

I have enjoyed one of the first pair of Focal Sopra No2 speakers that arrived stateside, driven by a smooth-sounding McIntosh power amp, the BE tweeters don't sound too bright at all.  I can and do listen to that pairing for hours at a time.

Having said that, I've auditioned the same model speakers driven by a "more contemporary"..."fast" amp and didn't find the sound as pleasing.  When I audition speakers I typically spend some "quality time" with the audition and felt that I probably couldn't listen to this "fast amp/Focal" pairing for as long as I can with the setup I have at home.

Like others have said, it really depends on the implementation.  Focal makes excellent Be tweeters that sound great, once they are broken in.  The first 300 hours are rough, extremely bright and metallic sounding but after that they gain a sweetness, while still being detailed.  

Revel uses SB Acoustics Be tweeters in the Performa Be line (328be/228be)if I am not mistaken and I think they are great. Less grain than the tweeters focal uses in the Sopra line which is also very good. Check out the water fall plots on stereophile of both speakers and the SB settles real quick and clean. But Revel might have worked some magic with the wave guide and motors. What ever is in the 328be (assuming SB) is pretty perfect. 

I have Focal Sopra 3's, in a properly treated room.  The Be tweeters are to my ears perfectly integrated with the other drivers such that I hear a coherent sound with plenty of detail, very transparent, yet without the tweeters calling attention to themselves.