I am only addressing USEF rules, not FEI.
In addition to the USEF (NOT USEA) rulebook https://www.usef.org/forms-pubs/KlV5…nting-division you need to look at “Annex 1” https://www.usef.org/forms-pubs/bGxa…s-saddlery-and
Waterford bits are not allowed for Eventing Dressage, ony straight, single jointed, or double jointed.
Rollers are not allowed for Eventing Dressage, with the exception of a tiny roller in the middle of the central lozenge (see number 5 on pg 2 of the Annex).
Baucher (referred to as “Hanging Cheek”) bits are legal for Eventing Dressage (the “Butterfly Baucher”, number 13 on pg 9 of the Annex, used to be illegal, but is now legal)
Within the legal bits, mutiple different metals are permitted.
I can’t suggest a dressage-legal alternative for a Waterford. But they are legal for the jumping phases.