It's not like Italy will be significantly changing their roads until the next time you get there. We used the Italy maps in our TomTom 910 last spring, they were flawless. Not once were they wrong on the roads we were on, and over two week, there were lots of miles put on the rental.

I would go with the TomTom, not only because it saves you a considerable amount of money, but because they worked so well for us.

Highly recommend to download the speed cameras too if it's an option for you.