Fred says that Tremoulinas is great attacking wise but a suspect defensively. As great a fullback is in attack, I won't want him unless he knows how to defend. And as great as he is, is he better in attack than Elia? I doubt it.
If it's true that Tremoulinas isn't good in defense then I'd rather have DC-Elia than Tremoulinas-Lanzafame. Bad defense in both cases, but at least a big attacking threat.