Im looking into adding new Mepro's to my M4, adding them to my M3, and also MAYBE adding a mini reddot to the my, something that will co-witness

Will the Mepro's be the same for the M3 & M4?

For the red dot, Im thinking either Dr Optic, Burris fastfire, or trijicon mini reddot reflex

What are your thoughts, opinions, and information?