More than one route can make a large ring. The decision turns on what the ring must survive.
A ring made from cord has its ends joined. It can avoid a full size mould and can suit a single unusual diameter or a time sensitive static seal. Ask how the ends are joined. An adhesive bond and a controlled hot vulcanised joint are not the same specification. Inspect the joint for a step, a gap or a change in cross section.
A compression step moulded ring, such as the CO.SM.O range, is moulded rather than cut and joined from cord. It can offer better consistency where a cord joint, dimensional variation or repeated movement is a risk. It is not the same product as a conventional full size moulding. Do not describe these rings as seamless, one pressing or spliced. The supplier does not publish the junction construction, so do not claim it.
For a static cover with forgiving geometry, joined cord may be a fair option after checking the duty. For movement, critical pressure or a cleanability requirement, ask for a technical review of the process and the exact compound before choosing. Cost alone is not a seal design criterion.
Related: large diameter O rings, vulcanised O rings in pressure or vacuum seals and the guides library.