My personal phone number is published here and there and so I often receive phonecalls from people looking for books and resources or asking questions. They always assume that they are calling an office and otherwise have no idea who they are talking to on the other end (not that they would know me anyway), and I'm glad for this because it results in some interesting conversations.
I just got off the phone with an older priest, now retired, who still says four extraordinary form public Masses every week and one ordinary form Mass on Saturdays, just to help people out who need the help. He finds himself constantly in the position of training musicians for both forms, and he told me that his own view is that it is much easier to train for the EF, mainly because the rubrics are clear, the signals are clear, the music doesn't dominate the Mass and instead takes its rightful place, you know exactly what is coming and how long things last, so you know precisely what to do, every Mass, every week.
It is different in most ordinary form Masses, he says, in which you never really know what the priest will sing, who will be walking around on the altar next, what the people expect, what will be sung or said and with what tune, how long actions will take, who will sit where and or what will happen. His impression is that it has been 30 years of confusion. There are so many variables and it one never knows what options are going to be chosen or defaulted to week to week. It varies from Mass to Mass, from week to week, from parish to parish. It is far too complicated to keep up, and it takes years for a musician to learn all the subtle signaling devices, and to anticipate the next option and choice.
It's just one priest's perspective but I thought it was interesting enough to share.