You dont have to deploy MSS ADD ON, You can upload roles directly from PFCG in NW 7.4
So basic question is are you planning to implement MSS ADD ON first?
are you implementing now?
If yes, then you should definately considered latest EHP7 fucntionality not only MSS EHP5 based one, try to activate all switctes for latest and get all functionaltiy as it would be better
But you need to see how it effects your current system