Tweeters - beryllium vs esotar

Ive owned both..I found that the Focal B tweeter to be on the metallic side,unnatural ,,,the Esotar2 tweeter IMO is more spot on

Just realized you wrote Brylliom in your post, but not title. did you mean Berrylium?
Berrylium is a very light metal and if fabrication was not an issue, would probably be good for those liking metal dome tweeters....I have always found them a little....metallic, if you will. Berrylium is difficult to fabricate because of some allergic / or poisonous reactions to it in some forms, like powders or filings.
Design / execution / fabrication trump any simple material choice concerns.
a properly executed silk dome is better than a poor metal dome.

Metalurically speaking, what (alloy?) is Esotar?

I carry 2 brands with Be tweeters (Revel and Focal), and no they dont offer much if any difference over the Esotar tweeter, which is a proprietary Dynaudio design (I also carry).

I think as you mentioned it more or less has to do with implementation which takes into consideration the cabinet design, crossover network, and the midrange/woofer designs. This will affect the overall sonic presentation more than just a fancy driver material alone.

I think Dynaudio is the best soft-dome tweeter currently on the market, while Revel and Focal probably make the best metal tweeters right now. Again Im saying not 1 solution is better or worse, just different. You would need to let your own ears decide this one.