All of these [pick your name] oils are whatever the manufacturer decided to make them from. The same or similarly named product from two different manufacturers, or even two divisions of the same company can be quite different. Likewise, teak, Danish, antique, rosewood, and tung oil finishes from the same company can be either identical or varying only in small proportions of the main ingredients -- thinner, oil, varnish.

As far as I know, most of them are either thinned varnish or thinned varnish + linseed oil. In either case, they are usually meant for an in-the-wood (non film-forming) interior finish.

The ability to inhibit moisture is proportional to the thickness of the applied finish. But I don't think you want a thick finish on this piece.

Oil, by itself, is not an effective moisture barrier. Some oils are even hygroscopic (attracting moisture). Some promote microbe growth.

The other thing is that most clear finishes break down with UV exposure.

One option is to just leave it to age.

Another option is a 100% solids UV-cured resin such as at the link below. I put it on my granddaughter's swing set 4 years ago after the factory finish degraded after the first year. It has been holding up well.

Here is a link that might be useful: One Time