If you expect your outline notes to go directly into the body of the associated document, then I don’t see a huge advantage, especially in light of the option I found in the Import/Export preferences. I mean, it is pretty easy to copy from Synopsis to body text, but Synopses are plain text only, so aren’t suitable if you need bold, underline, italics, strikethrough, etc…
Omni Outliner is a stellar outlining app with a number of features that are hard to beat.
Scrivener contains within itself a wealth of features, many of which can be taken advantage of in the outline view, but its flexibility makes Scrivener’s outliner merely superb. So really, it depends on how deeply you are into OO’s features during the majority of your outlining phase on any given project.