From what I found on the internet, non of the diamond tweeters use ferrofluid in the tweeters. It's used in the metallic tweeters in the other series.
Not sure where you found that information on D3s and D4 tweeters
Upgrade from B&W 802D1 to Focal Utopia Scala Evo
If you had the chance to upgrade from the B&W 802D1 to the FOCAL UTOPIA SCALA EVO, which would you choose and why?