They are all made by Rokinon. Their may be cosmetic differences, or even minor customization. I have customized and rebranded products made for my small business, they are aimed at specific markets that other companies do not serve, so I'm the only source. I also supply them to other retailers. Since I buy small quantities of 1000 or less, the biggest expense is custom boxes or packages which are printed in a minimum of 5,000 pieces, so 4,000 get tossed ( I keep a few for spares in case of shipping damage to the boxes)
This lens from Korean lens manufacturer Samyang is also sold in re-branded versions as Bower, Falcon, Polar, Pro-Optic, Vivitar and Rokinon 14 mm super wide angle lens. You may want to search around for these rebranded versions for best price. Optically and mechanically, they all appear to be identical.
However, Warranties may be different because they are sold under different private labels.
Check out the company called Elite Brands. They are actually the owners of the brand names Rokinon and Samyang as well as several others.
http://elitebrands.com/