Except in special circumstances, we have seen no evidence that a swivel solves any significant issues related to the retrieval or deploying of anchors.
It is known that cheaper swivels fail for several reasons related to poor engineering or poor manufacturing.
Therefore if you must use a swivel for any unknown reason and we have great difficulty in endorsing the practice, then a galvanized, cup/open swivel that is the same size as the chain will be too weak. Be sure to go up two sizes, and we’d also suggest choosing an eye-and-eye cup swivel so that you can attach a secure, quality shackle to each end. Steer clear of any low-priced, no-name stainless steel swivels, even if they’re oversized. In our opinion, no swivel should be attached directly to the shank of an anchor, because sideloading greatly reduces the safety factor. Unless your swivel or shackle can match 100 percent of the chain’s ultimate tensile strength at any angle of pull, it is not worth the risk.
If your anchor still doesn't come up in the right direction to your bow roller after aligning the Chain/Gypsy/anchor properly, you better use a Boomerang.
When using a Viking anchor, due to its design, you will never need to use a boomerang nor swivel, the anchor will always align itself in the right direction to the bow roller upon retrieval.