A C3 lance requires electronics totalling eight tons and eight crits and comes with a free TAG. A C3 company requires twenty-eight tons and as many slots total and carries four free TAGs.
A C3i lance also requires gear that takes up eight crits, but here it weighs in at ten tons total. A C3i company would come up to thirty tons and only twenty-four slots...but isn't actually buildable because C3i stops at a network size of six rather than twelve, so the best I get for that are two separate Level IIs that, while they can still work together just fine, can't share targeting data with each other. Also, if I want TAG capability here for some reason, I have to buy it extra.
Pretty much the only advantage of C3i is that it doesn't require -- and thus the network isn't vulnerable to the sudden loss or cutting off of -- one or more dedicated "master" units. Which is nice and all, but usually I'd rather take C3 precisely because it's easier to have a few dedicated specialist masters and then slap slaves on everything else than to find two and a half tons for C3i on every chassis in my outfit.