Good for when it first became available in early 80's for a collimator type, quick reaction sight (cutting edge then). What happens is that with both eyes open your mind superimposes both views together to place a dot on the target (strong eye looking thru tube where all you will see is a tritium powered red dot on a black background/ weak eye seeing unobstructed target/ background ). Still viable but not as efficient as what is offered today ( Aimpoints, EOTechs, ect...).
Both eyes open is the way to go anyway. You are more aware of your surroundings, pick up threats more quickly and are able to react to a changing dynamic situation more efficiently. Aimpoints, EOTechs are designed with every intent to be used with both eyes open as are the ACOGs to exploit the BAC (as was done with low/medium mag scopes well before the ACOGS where manufactured).