Beryllium Tweeters - Your Opinions & Comments ??

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.  

In general I don’t like metal tweets and prefer silk dome.  Something about the metal just sets me off.  But, hearing the Be tweets in the Magico Q7 sounded excellent to me with no bothersome metallic sound whatsoever.  Obviously it comes down to quality and implementation, but I would actually entertain a speaker with a Be tweet if the rest of the speaker really grabbed me.  I’ll also say the diamond tweet in the B&W 804D3 didn’t bother me either. 

BE comes with a karmic burden. It's toxic why use it? You may not get ill but what about the miner's, factory workers, or those in the future.