I think it's a bad idea. There will also be male models at the WTA end of the year championships in Madrid this year (if I am not mistaken). It's going to be hilarious.
The model ballgirls are a bit slow compared to the ballkids, which is understandable since they are much taller and not trained for this as well as the kids. I noticed Nadal was annoyed with them a couple of times when they didn't understand what he was asking. He didn't seem very impressed by their charms.
They are mostly good looking but I thought a couple of them looked anorexic.