Thanks jbaent and dona74 for your interesting references.
To be honest, I was worrying about the huge railings that seem to hide the view from balcony 1st or 2nd row. Apparently, the problem is not the view, it's the sound (and security disturbance if some people are in a bad mood ? ). What a challenge !
I'm seriously reconsidering my trip to Rome but I think I will go anyway because I already have my plane tickets.
Of course an awful acoustic is a pity but it's much better than nothing.
Only an extra show for me.