beryllium vs diamond

Oh kosst-amojan, there is no question that ribbons disperse better than many if not most ESLs. But if the ESL is designed correctly this is not a problem. Everywhere else there is no comparison first because there is no crossover.  Second, the diaphragm has less than a 10th of the mass.
Third, the diaphragm of an ESL has uniform drive right down to the molecular level and is push pull throughout. 
If you were to sit down in front of Soundlabs Majestic 845s driven by say Atma-Sphere MA-2s even without subs you would be dumbfounded. Your response would be, "How can a speaker do that!" You would probably even wet your pants or diaper or whatever.

georgehifi, it is not a matter of opinion. That ESLs are better is a matter of fact for the reasons I stated above.  I love Maggies but they can not hold a candle to a big ESL. 

The N28-BER by Transducer Labs that Fritz uses in his Carrera speaker is the only one I've heard that I think I could live with.  BTW, TL describes this on their website as pure beryllium.

I have no experience with diamond tweeters, however I recently picked up a pair of second hand  Focal Electra 1008 BE speakers and am using them in a near field setup in my computer room, driven by my Audio Research VSI 55 integrated and they sound fantastic.  I don't care for "bright" speakers and the Focals are not to my ears.  They are very detailed, but the top end doesn't call undue attention to itself.  I don't play them super loud, but have tried them out in my main system and in many ways they bested my Legacy Audio Focus 20/20's, but they are too small for that large of a room.

There are some "reviews" (sales pitches) on Upscale Audio's youtube channel on a couple of the Focal speakers that use the BE tweeters.  You might get more technical info from those.