Here's a review (perhaps "demo" would be a more accurate term) of the Delangle mouthpiece from
sax.co.uk:
They employ their usual approach of never, ever having a classical player test any equipment, even horns or mouthpieces that are designed by their manufacturers with the classical market in mind.

They also tend to be reluctant to say anything significantly negative about the products they demonstrate, since their ultimate goal is sales, not disinterested commentary. The best thing about this video is that Jim Cheek is playing a black lacquer Series III Jubilee alto, which is clearly the horn of choice.
The mouthpiece review from
thesaxophonist.org is a bit more systematic and objectively oriented, although the way the reviewer describes the mouthpiece's playability discourages me from trying one (especially given the high price):