Well, the horn is different. And sometimes just being different makes it unattractive.
I spent many years in Europe playing alongside these horns. While I agree with Dave that these horns lend a nice melodic sound, they do have intonation quirks that just aren't that severe in most pro-level horns I've played on. Stuffiness and ergonomics also weigh into it too. Meh. I'm too far gone to adapt to something new like that, so a horn like that has absolutely no appeal to me at all.
U.S. Army, Retired (built mid-1950s)
Adams E2 Euph (built 2017)
Boosey & Co. Imperial Euph (built 1941)
Edwards B454 Bass Trombone (built 2012)
Boosey & Hawkes Imperial Eb tuba (built 1958)
Kanstul 33-T lBBb tuba (built 2010)