They sell them under many different names. Samyang does not warranty them when they are sold under a different name, they sell them in quantity for a low price, and the 2nd tier company sets their selling price and warranty terms. You must get repairs done by Rokinon, for example. Its generally not a big deal.
I bought a Rokinon branded one, they have US distribution rights. The one I received was junk quality, it went right back.
They are supposedly FF lenses, but the instruction sheet I received said that the lens was optimized for use on a crop body.