Although the text of the law is arguably a little confusing, the ATF was made official statements that make it pretty clear. IF the weapon is assembled with enough US parts it's not subject the importation requirements, then it can have all the evil features available. Period, end of story (as long as it doesn't run afoul of any of the long standing NFA crap of course)
I've found gun dealers to without a doubt be the worst source for accurate gun info there is. Well, maybe with the exception of the local range nazi/know-it-all types, but they're just trying to become dealers probably... You'd think people in the business would actually know what the heck they're talking about, but nooooo... Makes no sense really, if I'm not fairly sure I don't open my mouth, or I at least make it known I'm not sure. But gun dealers will swear up and down you're 100% wrong even in the face of direct proof. It flies in the face of logic... I guess they have to deal with know-it-alls all the time too, but you'd think they'd at least be open to seemingly well informed customers when they're not sure on an issue, and then check for themselves later. But again, noooo...