Tweeter Differences

What is the advantage or disadvantage of a ribbon vs a Diamond or Beryllium tweeter in a speaker?
Ribbon has a distinct radiation pattern. It suffers from distortion at lower frequencies.

Berylium is good but may suffer from undamped ringing in the audible band ( as does most rigid material )

Diamond is kind of a stiffened fabric dome a kind of composite material design - so it has some internal damping which is good but also extremely rigid - to me this would be best of the three - however it is ridiculously expensive for what it does - who needs anything above 15 Khz anyway?
SOME ribbons may distort at "lower" freqs. Ribbons like the Magnepan can go pretty low, allowing for uncrossed over vocal range purity.

Once you have heard them there is no going back to conventional tweeters
I believe all the current diamond tweeters are made with CVD technique similar to what semiconductor industry uses to deposit thin films. There is a substrate required for CVD to deposit on.

Beryllium is extremely stiff and has good damping property, significantly better than Ti or Al. Audible breakup is well above 50k hz.

In real life listening, some will prefer diamond while some will prefer Be, they just sound "different" though both are better than any conventional hard dome like Ti, Al, or Al2O3 (ceramic).