We all saw that in the 442 we are playing, where some parts of build-up relies on both strikers, Trez just doesn't fit in and getting the hottest striker in Serie A instead of him is just sick deal. In Udinese everyone have really small wages (I think Tonio is making 1.4m per season or smth like that), so we might end up paying 4-5 millions in total for his wages, which pretty much makes up for the transfer fee, since we were paying 9 millions for Trez wages.
Relying on big strikers to score on set-pieces is fine and all, but with di Natale we might be capable to play some football in attack after some years.