Caldirola is a good 'foil defender' as I Would call it.
As we've seen, all the best defensive partnerships are created by two dissimilar centre backs. And it's not just as easy as saying 'hes a good defender', 'hes a bad defender'.
What it is about is a player's ability to work with his defensive partner, too. You can take two great centre-backs and have a poor partnership, and similarly, two average ones and have a great partnership.
Luca's very talented at working around his team mates, providing a 'safety net' when they do something more aggressive, things like that.
I think Caldirola is an absolutely top defender - look at what he did to Brescia when he first went there.
I don't know enough about Benedetti's style, but between Ranocchia-Juan, Juan-Caldirola, Caldirola-Benedetti, Ranocchia-Benedetti, I think we're set for a few years.
The question, of course, is how we can accomodate 4 good young Centre Backs. That's not so obvious to me. Even if we play them all in the same team as 3 CB back line, Ranocchia Juan and Caldirola all play the LCB position (primarily) - not to imply, of course, they can't learn.