Usher isn't claiming the domes to be pure diamond domes. Here's some info from their site:
"...laminated diamond-metal-diamond structure, which consists of a proprietary metal alloy base layer coated with an amorphous diamond-like carbon layer (pure diamond is carbon atoms arranged solely in sp3 bonds; amorphous diamond-like carbon has mixed sp3 and sp2 bonds to achieve its desirable properties) on both sides. The base metal layer of the Diamond DMD dome tames all the diamond layers' unfavorable sonic traits and brings out the best of both materials."
There are many excellent tweeters available regardless of material used. The Usher BE tweeter was easily one of the best tweeters I've heard even though it was mostly titanium.
"...laminated diamond-metal-diamond structure, which consists of a proprietary metal alloy base layer coated with an amorphous diamond-like carbon layer (pure diamond is carbon atoms arranged solely in sp3 bonds; amorphous diamond-like carbon has mixed sp3 and sp2 bonds to achieve its desirable properties) on both sides. The base metal layer of the Diamond DMD dome tames all the diamond layers' unfavorable sonic traits and brings out the best of both materials."
There are many excellent tweeters available regardless of material used. The Usher BE tweeter was easily one of the best tweeters I've heard even though it was mostly titanium.