It's difficult to rate aromas, since it is SO subjective. In my opinion, Devilwood has a nice fragrance, but not nearly as sweet smelling as the O. fragrans. It has quite a different appearance, too, so be prepared for that.

ditto what rhizo says. in fact, my o. americanus plant is not nearly as robust as the o. fragrans, appearing to struggle more. fragrance is much less intense, perhaps due to the smaller number of flowers. it is not noticeable to me unless i position my nose close to the flowers.
if you are concerned about naturalization of the asian species, i doubt you will ever see that.

I'm trying to find some seeds of Osmanthus americanus (Devilwood)... are there anyone who could help!!??? :O)