Argus - are you in the US? If you are anywhere outside of Australia, you can forget about owning a L. o. barroni. They are just not available to the hobby.
In Australia, they are considered vulnerable, and my understanding is that they are fairly restricted to private collectors there as well. I do know some breeders have them there, and that the regulations are regional - but I don't know the details.
Like most species olives do have a variance in attitude, most seem to be pretty calm. Mine are extremely gentle - I have heard stories of aggressive babies... but it is all 2nd hand information. Anyway, personalities certainly will vary, but with proper regular handling, they should settle down. I would hope any that don't are in the care of a very experienced keeper. A 12' aggressive olive would certainly be a handful.