12 limits your maximum working distance and forces you to use bigger fonts.
Bigger fonts force you to scroll faster because you can't show as many words on the screen at the same time. Which makes reading choppier and harder for the talent, particularly the more inexperienced person or one who's doing this for the first time... like a non-actor, perhaps an office person in a corporate setting... just the worst kind of person to be put into that position.
Prompters are not just for text: we use them a lot to show things like powerpoints so the presenter can keep eye contact with the TV audience but still see their slides. It can make a big difference.
You may be limited to 12 by circumstances not covered in your first post. If not, seriously consider going bigger.