Both will block transmission of blue and green. The difference is where in the visible spectrum they begin to allow transmission.
The Roscoe #19 Fire begins transmitting in the orange/amber region, also allowing everything lower in frequency (such as red) to pass. Since sodium orange is the color we really want from a Duplex (and nothing higher such as greens and blues) this material is a good match.
The Rubylith doesn't begin transmitting until you get down to red. It blocks everything higher than red, including orange/amber. Since the LEDs are mostly red to begin with, it doesn't matter that the material also blocks orange/amber. It's the red we really want.
The reason for choosing the Roscoe for the sodium light source is that it largely passes the desirable orange/amber, while the Rubylith does not. Using Rubylith on the sodium would unnecessarily darken the orange/amber output for no additional benefit, as both filters equally remove the undesirable greens and blues.