|The coating on the Vivitar front glass is more blue,|
the other two has a similar coler, more pink.
With the screw-on adapter, 1:1 ratio can be achieved. Without the adapter, the lens can be uses as a 100mm prime.
Besides the brand names on the front plates, another difference I notice is the coating colors on the front and rear glasses. However, I am not sure if the color variation is among the brand names or individual copies,