I tried them and the sound/sustain was indeed pretty incredible. They are wound with nylon, so there's a definite texture to them, and like the site suggests, once you put them on don't expect to be able to take them off and reuse them as the nylon winding comes undone at the ends. Unfortunately I tried it on a not so great tenor (an old Kala that ended up having some warping issues) so I don't know if I can say I got the best out of them.
They are kind of expensive to experiment with since you can't move them around.