I've been encountering a lot of verbs in the Core6k recently that have these "notes" that say they can be either a regular す verb or act as a する.

達する／達す
属する・属す

There are a couple others I've seen but I can't think of them off the top of my head.

Is choice of which way to use them largely personal preference/dialect?

The -す versions are older, and if I'm not mistaken, more formal and literary, so you would see them more often in written Japanese, particularly documents, song lyrics and whatnot than you would see them in spoken or casual Japanese.