If they think that using self mortification is pare of their religion, and is something that they need to do, than by all means they should do this. This is all up to them and their faith, and that is what they need to go off of, just what they believe.
I believe Opus Dei should continue to use self-mortification as a means of remembering Christ's suffering, given that it is one of the tenets of the religion and sect. This is usually performed through fasting, periods of silence, or maybe sleeping without a pillow, or sleeping on the floor. Self-mortification is actually pretty common in religion so there's no reason to look down on it. If anything, it sounds worse than it really is in this case.
I personally think that Opus Del should not continue to use self mortification as a meaning of remembering Christ's suffering because it can affect the people of Christ and it could put a heavy weight on that individual. I personally think that Opus Del should not continue to use self mortification as a meaning of remembering Christ's suffering because it is remembering something horrible.
While the self-mortification definitely makes a statement, the point of Christ's death was supposedly so that we wouldn't have to suffer. He died and was beaten for our sins, who are we to carry out the same punishment on ourselves? That said, freedom of religion/speech/choice should be obligatory and if this is the way individuals are choosing to worship, they should not be hindered.
No, Opus Dei should not use self -mortification as a means of remembering Christ because there is nothing truly supporting it in the Bible. Merely because it is touched on does not signify it as a reason to focus directly on it. I think it is both bad for the members and publicly does not help their cause. Self-mortification is not support in the Bible.