Warning: Diamond tweeters can be the worst engagement token ever…regardless of how well your fiancé tolerates your audio hobby you can get those utterly misunderstood, and you look like a jerk on the Jumbotron. I also agree that the diamond coated/berellium/titanium/soft dome/hard dome/thunderdome/folded foil/air transformer/blow torch vapor/plasma flame gas bag hype of tweeter material is meaningless except for what a speaker designer does with these things…I've heard vintage soft domes sound absolutely crystal clear and metal domes sound "meh" and dull…I do like screened ones that resist poking by drunk partiers, or deep horns that resist everything but maniacally sprayed champagne.
