The early Miller One Triggers has the selector on the safety like the 3 position safety on some L.C. Smiths.
I have a 1927 Ideal Grade with this type of trigger with the safety selector.
Later ones had the selector alongside the trigger, similar to a HOT.
I am not sure if more wood has to be removed between the side locks as it does for the HOT and on the L.C. Smith Featherweights, metal has to be removed from the top tang area for the actuation of the second firing.
In order to tell if it is a real Miller, in the case of the later ones, I guess you would have to take the gun agart and look.
Dan May of Classic Gun Stocks, has the exclusive rights to the Miller One Trigger now.