Ah, I've actually been looking at this and have yet to find what I consider robust data. Doesn't mean it doesn't work - just that I myself am not sold.
What I did find actually points to it work better as a co-preservative, but not sure why. Maybe because it's effective in a narrow pH range, or that it's only effective against some, or because it ain't all that to begin with.
it's just EOs, which is why the FDA says it can be included on the label as fragrance.
I certainly wouldn't use it without strong data, but that's just me. So if I did try it - I'd have to have my products go through challenge testing. Challenge testing isn't simply making a product and having it then tested for the presence of microbes - it's making product, introducing germies, putting it through various stresses like freeze/thaw cycles, water added (as from wet fingers) and such to see if it can actually prevent the growth of the microbes a consumer might get into it along with conditions it might face. Just using it and saying "I didn't see any mold growth" or "it looked fine even after a few months" is not proof it works. But like I said - that's just me.
So, if anyone does try it and has their products tested - please report back!