Coach, the one I have came from UNV. It is the 50mm and the adapter makes it fit very well on the Photon XT. It really improves the clarity of the night vision picture as well as doubling the magnification. It would not be useable for a calling outfit, but works great on a bait site or feeder. It does reduce the light gathering ability somewhat as compared to the scope when it doesn't have the doubler attached. I am using a T-20 IR light with 3 powers of 15%, 50%, and 100% plus the ability to focus the IR. I know that I could shoot a coyote at 250 yds with the doubler installed and the T-20 set on 50% power and zoomed pretty tight. I haven't really gauged how much farther I might be able to make a shot at 100% power, but guessing about 350 yds. My bait site is set up at 145 yds. so it would be a fairly easy shot with 50% power.
I don't think it would work well to try using the Photon both ways. I've tried that a little bit because I thought I might use it for calling without the doubler and then put the doubler back on for bait site shooting. The X,Y coordinates are not the same with the doubler installed as they are without. So you would need to reset the coordinates each time when switching back to the doubler. I marked mine so that I can screw the doubler back on at exactly the same tightness each time, but I'm still not comfortable (yet) that I can do that without having to recheck zero by shooting it each time.
I have several videos on youtube showing the different lighting and distances with and without the doubler. I'm giving you a link to one of them and you should be able to find the others from that.