I finally tried the Loki Prime the other night, and it is lovely. At one point I was scouting for an assault wave and picked off three damaged mechs as they tried to limp home, all in the course of about a minute.
In my opinion, C3 on its own is good but not great. People will get a bit of early warning / extended lock range, but I think it's limited in practice unless you manage your forward position extremely well. What's *really* good is C3 + BAP/BHP + GECM. You'll see BAs from hundreds of meters away, which means everyone in your net will see them too. You'll spot APCs, even when they're powered down, which means anyone in your net will too. You'll detect GECM battle formations before they'll detect you, if only by a few hundred meters, which means fewer surprises for your teammates. Add in NARC and you can turn the whole game around.